Water changes, how?

Hello everyone.

I just wanted to ask about doing water changes to my tank. I know water changes are very important but its been 3 weeks since my tank has been running with lovestock in it and i didnt do any water changes due to the fact that i dont whats the proper way and what tools do i need?

Plus when water evaporates from the tank what do i do? Should i just add tap water?

I have an 8.5 gal (32 ltrs approx) tank.

Thanks!!