Brackets (Parentheses)
Brackets are symbols used in pairs to group things together.
Types of brackets include:

When you see things inside brackets you do them first (as explained in Order of Operations).
Example: (3 + 2) × (6  4)
The parentheses group 3 and 2 together, and 6 and 4 together, so they get done first:
(3 + 2) × (6  4)  = (5) × (2) 
= 5×2  
= 10 
Without the parentheses the multiplication would be done first:
3 + 2 × 6  4 = 3 + 12  4 = 11 (not 10)
When you do more complicated grouping it is good to use different types of brackets:
Example: [(3 + 2) × (6  4) + 2] × 4
The parentheses group 3 and 2 together, and 6 and 4 together, and the square brackets tell you to do all the calculations inside them before multiplying by 4:
[(3 + 2) × (6  4) + 2] × 4  = [(5) × (2) + 2] × 4 
= [10 + 2] × 4  
= 12 × 4  
= 48 
Curly Brackets
Curly brackets {} are used in Sets:
Example: {2, 4, 6, 8}
Is the set of even numbers from 2 to 8