How do I dress my baby using short sleeved onesie vest/sleepsuit?!

I bought a pack of these but didn't think about how I would dress the baby?
Are they to be worn under a full length long sleeve sleep suit, or should I put him in it with little joggers and a cardigan? 
If they're to be worn underneath another sleep suit then what's the point in them being patterned? 
Argh I'm so confused!! Please help! 😂