In JavaScript, the let keyword is used to declare variables with block scope. Block scope means that the variable is only accessible within the block of code where it is declared. This is in contrast to the var keyword, which has function scope. Here are some ways you can use let in JavaScript:

1. Variable Declaration:

   javascript
   let x; // Declaring a variable named 'x'
   

2. Variable Initialization:

   javascript
   let y = 10; // Declaring and initializing a variable named 'y' with the value 10
   

3. Block Scope:

   javascript
   if (true) {
     let z = 5;
     console.log(z); // z is accessible within this block
   }
   // console.log(z); // This would result in an error because z is not defined in this scope
   

4. For Loops:

   javascript
   for (let i = 0; i < 5; i++) {
     // i is only accessible within this loop
     console.log(i);
   }
   // console.log(i); // This would result in an error because i is not defined in this scope
   

5. Re-declaration in the Same Scope:

   javascript
   let a = 3;
   // let a = 5; // This would result in an error because a is already declared in this scope
   

6. Shadowing:

   javascript
   let b = 10;
   
   if (true) {
     let b = 5; // This 'b' shadows the outer 'b' within this block
     console.log(b); // Outputs 5
   }
   
   console.log(b); // Outputs 10, the outer 'b' is not affected by the inner one
   

7. Temporal Dead Zone (TDZ):

   javascript
   // console.log(tempVar); // This would result in a ReferenceError
   let tempVar = 20; // The variable is declared but not yet initialized, it's in the TDZ until this line
   console.log(tempVar); // Outputs 20
   

These are some common use cases for let in JavaScript. It's important to note that let has block scope, so variables declared with it are limited in their visibility to the block in which they are defined.