How would I attach a part to a player when the spawn into my game? For instance, on a survival game players will usually automatically spawn with a backpack
You're going to want to weld the parts to the player (refer to: http://wiki.roblox.com/index.php?title=Weld) The torso would be Part0 and the part anchoring to it would be Part1..its a little tricky to get the hang of, just experiment with different things and you should get it working.. just remember to leave the armor or whatever un-Anchored otherwise you won't be able to move..Make a model and put the primarypart of the model to be Part1
These two are your friends, Welds
http://wiki.roblox.com/index.php?title=API:Class/Weld
Use a script to get all children of the object, and then weld them to the torso of the player. A bit tricky at the start but once you get the hang of it , it will be easy.