Quote: "can you take characters from other games you have on your computer? "
Yes, importing custom charcters is possible, but you will need permission to re-distribute other people's media.
So, either the products license has to allow for you to use it or you need their written permission.
Not many are going to let you re-distribute the media unless it is protected and you are releasing it free of charge as a fan-based tribute.
But for making your own personal games for fun that you don't intend to sell...check out
FragMOTION and
MilkShape 3D.
Both of those were made to modify games, so they can handle most of the popular game model formats!
Plus, they are both really affordable ($35 and $25), so you can buy them both for about $60. (I use both)