What is your summoner name, Clutch? For now, mainly use your IP to buy new champions that appeal to you. Just keep trying out different champions (take advantage of the free week champs) and see what you like. Then if you find a role you like (support/tank/carry/bruiser/etc.) then you can buy other champs of that role. Later on down the road (lvl20+) you will begin to buy runes with your IP, but that is a ways off. As for RP, you could use it to buy a champ you really want but don't have the IP for, you could save it for later, or, if you see a skin on sale of a champ you own and like to play a lot, you can use the RP to buy the skin.