Ive read the attributes sticky at the top.. It just confused me even more

I have read countless threads on this forum which confused me even more.

I am building a shopping cart to sell tshirts...

all i want to do is add a size option on every product.. small, medium, large, xlarge.
this selection has to be required but has no effect on price..

can somebody please, pleeease give me a step by step on how to do this because i just keep getting totally lost.

If possible i want this to be automatically added to every product so i dont have to keep adding it every time i add a new tshirt.. is this possible?