Caitlyn in a Nutshell is a counterpick to most of those early game bursty Ad Carries. She has a super long attack and skill range which allows her to poke from a distance and get out of range of those Annoying Carries like Vayne and Miss Fortune whose range are relatively short.

When Picking Caitlyn there arent many counters to her unless you have a non ranged AD Bottom. Someone who can really ignore your burst like Pantheon. Or Kill you before you can burst Like Riven or the Notorious Vi.

Caitlyn Overall isnt a hard carry to use. Her Range and Passive allow her to farm easier making her snowball into middle and late game