In a motherboard with two RAM slots, you'll just put your first stick of RAM into Slot 1 and a second stick into Slot 2. If you just have one stick, you don't have to fill Slot 2. In the case of a motherboard with four RAM slots, it's probable you'll want to install your first RAM stick into the slot labeled 1.

Does it matter what slots I put my RAM in?

A common misconception about RAM is that you can put any RAM into any slot. You can do that, but it won't work, or it will work ineffectively. If you have four RAM slots, always buy matched pairs of RAM (two sticks from the same company, same speed, and same capacity) for the best results.

Which RAM slots to fill first?

Fill slot 0 (or 1) first, then the other slots sequentially as you add modules. If you are installing memory in a dual-channel memory motherboard, install memory modules in pairs, filling the lowest numbered slots first.