How should I play the pit mu I completely suck at it I tried camping him but his arrows ***** me they come out too fast.
You can start getting good at it by getting used to dodging arrows and simply going in for the Ftilt range. Once in the ftilt range your presence is threat enough alone to force him to do a defensive reaction (usually dash attack, fsmash, roll or dash grab).
When you get used to paying attention to individual Pit habits when arrowing and moving about, you can learn where you want your C4's (cut down their camping-viable spots), when to pull nades, when to throw nades (pulling and throwing with no pause to shield between is risky usually), and what to do when you do get past all the arrowing.
Ultimately a cooked, normal lob to their side before they get on stage...or a C4 placed on the opposite side of the stage...can really cut down their camping payoffs. Close range is your friend against Pit. But you still have to actually outplay pit when you do fight close range. If they're very aerial don't underestimate your Bair and uptilt.
Things to keep in mind
1) Timing of Arrows (usually determined by purpose, like they react to your nade pin pull or your shield drop)
2) Defensive reaction when you get in ftilt range, and how to beat it with at least 20% damage punishment
3) How to ruin their favorite spots
This is the case also for many matchups that tend to semi-outcamp Snake. A well cooked, lobbed grenade or a well place C4 can really ruin their day.
In response to Kuro:
Running in with a nade and blowing yourself up should work once or twice...but there are a lot of adaptive reactions to that which will punish you back more than you expect.