To create assets you will need to use a modeling tool, such as Maya or 3DStudio. It also takes a moderate amount of skill with texture art and 3D modeling. For a character you also need some skills at model rigging and animating.i cant figure out how to make my own characters or assets
To create a basic character model with bones and basic range walking/running/jumping animations, if you were already experienced you could get everything blocked in place with a day or so of actual work --- and that's knowing what you are doing. To move from a blocky model with blocked-in animation over to make a good looking character with a broad range of good looking animations can take several weeks of combined modeling, texturing, and animation work.
The Unity forums have many good lists of free assets and pre-created and pre-animated character models.