I bought a pack from marketplace link below:
I thought the characters would come put together, fully animated. I don’t know what to do with all these parts? How do I put them together? Can I just swap out standard humanoid skeletal with the new mesh? If so how? Help Please!
Judging by the asset’s description it seems that you’ll have to do “retargeting”, as described here: https://docs.unrealengine.com/en-us/Engine/Animation/RetargetingDifferentSkeletons
Otherwise you should ask the creator of the asset for step by step instructions, it would be basic courtesy for a paying customer.