Maths

For the past three weeks we have been learning about expressions, equations and variables. I know that a expression is a sum with no equal sign. For e.g:
2 + 2

I also know that a equation is a sum with a equal sign. For e.g:
2 + 2 = 4

I also know that a variable is a letter that represents a changing value. For e.g:
A number minus 3
= n - 3

To increase our knowledge on algebra we played games on education perfect. I think that I am getting the hang of it but I still need a bit of help, so next I would like to learn more about variables.