Sharon, I've never used a trainer so can't speak to that. I did use a character editor once.
That was a separate program. You added it to the game folder (I think that's where it went, it's been awhile.) Using that program, you could open your character up and change all sorts of stats, make them unable to die, give them the best armors, unlimited health potions, the best gear, etc. I had fun with it until I did it so many times it broke my game, which was something that my son warned me might happen if I changed the character too often.
I know lots of folks use these with great success though. I think I just had a bit too much "fun" with the one I used. I believe a trainer is the same, but I could be wrong.