diff --git a/solutions/collections/String.md b/solutions/collections/String.md
new file mode 100644
index 0000000..d6fcdd7
--- /dev/null
+++ b/solutions/collections/String.md
@@ -0,0 +1,114 @@
+1.
+```rust
+fn main() {
+    let mut s: String = String::from("hello, ");
+    s.push_str("world");
+    s.push('!');
+
+    move_ownership(s.clone());
+
+    assert_eq!(s, "hello, world!");
+
+    println!("Success!")
+}
+
+fn move_ownership(s: String) {
+    println!("ownership of \"{}\" is moved here!", s)
+}
+```
+
+```rust
+fn main() {
+    let mut s: String = String::from("hello, ");
+    s.push_str("world");
+    s.push('!');
+
+    borrow_string(&s);
+
+    assert_eq!(s, "hello, world!");
+
+    println!("Success!")
+}
+
+fn borrow_string(s: &str) {
+    println!("ownership of \"{}\" is moved here!", s)
+}
+```
+
+2.
+```rust
+// FILL in the blanks
+fn main() {  
+   // get a slice of String with reference: String -> &str 
+   let mut s = String::from("hello, world");
+
+   let slice1: &str = &s; // in two ways
+   assert_eq!(slice1, "hello, world");
+
+   let slice2 = &s[0..5];
+   assert_eq!(slice2, "hello");
+
+   //Note! The type here cant be `&mut str` due to `push` is ONLY defined on String type and its mut reference: `&mut String` !
+   // So you can't use `s.as_mut_str()`
+   let slice3: &mut String = &mut s; 
+   slice3.push('!');
+   assert_eq!(slice3, "hello, world!");
+
+   println!("Success!")
+}
+```
+
+```rust
+fn main() {  
+   let mut s = String::from("hello, world");
+
+   let slice1: &str = s.as_str(); 
+   assert_eq!(slice1, "hello, world");
+
+   let slice2 = &s[0..5];
+   assert_eq!(slice2, "hello");
+
+   //Note! The type here cant be `&mut str` due to `push` is ONLY defined on String type and its mut reference: `&mut String` !
+   // So you can't use `s.as_mut_str()`
+   let slice3: &mut String = &mut s; 
+   slice3.push('!');
+   assert_eq!(slice3, "hello, world!");
+
+   println!("Success!")
+}
+```
+
+2.
+```rust
+fn main() {
+    let s = String::from("hello, 世界");
+    let slice1 = &s[0..1]; //modify this line to fix the error, tips: `h` only takes 1 byte in UTF8 format
+    assert_eq!(slice1, "h");
+
+    let slice2 = &s[7..10];//modify this line to fix the error, tips: `中`  takes 3 bytes in UTF8 format
+    assert_eq!(slice2, "世");
+
+    println!("Success!")
+}
+```
+
+3.
+```rust
+// FILL in the blanks
+fn main() {
+    let mut s = String::new();
+    s.push_str("hello");
+
+    // some bytes, in a vector
+    let v = vec![104, 101, 108, 108, 111];
+
+    // Turn a bytes vector into a String
+    // We know these bytes are valid, so we'll use `unwrap()`.
+    let s1 = String::from_utf8(v).unwrap();
+    
+    
+    assert_eq!(s, s1);
+
+    println!("Success!")
+}
+```
\ No newline at end of file
diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index ea9e0b6..c53ec43 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -28,10 +28,10 @@
   - [Traits](generics-traits/traits.md)
   - [Trait Object](generics-traits/trait-object.md)
   - [Advanced Traits](generics-traits/advanced-traits.md)
-- [Collection Types todo](collections/intro.md)
+- [Collection Types](collections/intro.md)
   - [String](collections/string.md)
-  - [Vector](collections/vector.md)
-  - [HashMap](collections/hashmap.md)
+  - [Vector todo](collections/vector.md)
+  - [HashMap todo](collections/hashmap.md)
 - [Type Conversion todo](type-conversion.md)
 - [Result and panic todo](result-panic/intro.md)
   - [panic!](result-panic/panic.md)
diff --git a/src/collections/intro.md b/src/collections/intro.md
index 1bdd607..db8e456 100644
--- a/src/collections/intro.md
+++ b/src/collections/intro.md
@@ -1 +1,6 @@
 # Collection Types
+Learning resources: 
+- English: [Rust Book Chapter 8](https://doc.rust-lang.org/book/ch08-00-common-collections.html)
+- 简体中文: [Rust语言圣经 - 集合类型](https://course.rs/basic/collections/intro.html)
+
+
diff --git a/src/collections/string.md b/src/collections/string.md
index 2c0923c..fe96e82 100644
--- a/src/collections/string.md
+++ b/src/collections/string.md
@@ -1 +1,111 @@
 # String
+`std::string::String` is a UTF-8 encoded, growable string. It is the most common string type we used in daily dev, it also has ownership over the string contents.
+
+### Basic operations
+1. 🌟🌟
+```rust,editable
+
+// FILL in the blanks and FIX errors
+// 1. Don't use `to_string()`
+// 2. Dont't add/remove any code line
+fn main() {
+    let mut s: String = "hello, ";
+    s.push_str("world".to_string());
+    s.push(__);
+
+    move_ownership(s);
+
+    assert_eq!(s, "hello, world!");
+
+    println!("Success!")
+}
+
+fn move_ownership(s: String) {
+    println!("ownership of \"{}\" is moved here!", s)
+}
+```
+
+### String and &str
+A `String` is stored as a vector of bytes (`Vec<u8>`), but guaranteed to always be a valid UTF-8 sequence. `String` is heap allocated, growable and not null terminated.
+
+`&str` is a slice (`&[u8]`) that always points to a valid UTF-8 sequence, and can be used to view into a String, just like `&[T]` is a view into `Vec<T>`.
+
+2. 🌟🌟
+```rust,editable
+// FILL in the blanks
+fn main() {  
+   // get a slice of String with reference: String -> &str 
+   let mut s = String::from("hello, world");
+
+   let slice1: &str = __; // in two ways
+   assert_eq!(slice1, "hello, world");
+
+   let slice2 = __;
+   assert_eq!(slice2, "hello");
+
+   let slice3: __ = __; 
+   slice3.push('!');
+   assert_eq!(slice3, "hello, world!");
+
+   println!("Success!")
+}
+```
+
+### UTF-8 & Indexing
+Strings are always valid UTF-8. This has a few implications:
+
+- the first of which is that if you need a non-UTF-8 string, consider [OsString](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html). It is similar, but without the UTF-8 constraint. 
+- The second implication is that you cannot index into a String
+
+Indexing is intended to be a constant-time operation, but UTF-8 encoding does not allow us to do this. Furthermore, it’s not clear what sort of thing the index should return: a byte, a codepoint, or a grapheme cluster. The bytes and chars methods return iterators over the first two, respectively.
+
+2. 🌟🌟🌟 You can't use index to access a char in a string, but you can use slice `&s1[start..end]`.
+
+```rust,editable
+
+// FIX errors
+fn main() {
+    let s = String::from("hello, 世界");
+    let slice1 = s[0]; //tips: `h` only takes 1 byte in UTF8 format
+    assert_eq!(slice1, "h");
+
+    let slice2 = &s[3..5];// tips: `中`  takes 3 bytes in UTF8 format
+    assert_eq!(slice2, "世");
+
+    println!("Success!")
+}
+```
+
+
+3. 🌟🌟🌟
+> Tips: maybe you need `from_utf8` method
+
+```rust,editable
+
+// FILL in the blanks
+fn main() {
+    let mut s = String::new();
+    __;
+
+    // some bytes, in a vector
+    let v = vec![104, 101, 108, 108, 111];
+
+    // Turn a bytes vector into a String
+    // We know these bytes are valid, so we'll use `unwrap()`.
+    let s1 = __;
+    
+    
+    assert_eq!(s, s1);
+
+    println!("Success!")
+}
+```
+
+### Representation
+
+
+
+
+
+### Common methods
+
diff --git a/zh-CN/src/generics-traits/advanced-traits.md b/zh-CN/src/generics-traits/advance-traits.md
similarity index 100%
rename from zh-CN/src/generics-traits/advanced-traits.md
rename to zh-CN/src/generics-traits/advance-traits.md