How can I use assignment operators in Javascript? I'm really confused

Question

Assignment operators

Answer 1

Martin Taylor there were some that were like this
+= -= *=
What are these?

Answer 2

These are a equivalent to
a = a + b
a = a - b
a = a * b

Example:
var a = 2;
var b = 4;
a += b //6
a = a + b //6