Basic trainer is just a memory editor. You can look up tutorials on memory editing in VB. You might even be able to find some specific to GTA games here, in the GTA Modding \ Tutorials section. The only real difference for other games will be different addresses for all the variables. If you can find what these are, you can use them. You can also look for these addresses yourself. There are some memory editors out there with search capabilities.
Unfortunately, I can't help you with any more specific information, since I haven't touched VB since school.
I haven't actually tried it, but I did look at what it does. It's a neat concept.
Usually, when people say "trainer" they mean a program that prevents health or ammo from going down, and things like that. That's usually achieved via memory editing. If you mean something different, could you please explain exactly what you want your program to do.
Just tried the trainer that you linked to above but it didn't work! It gave me an error: Cheat Code Typer (Full) has stopped working. This was despite trying to run the app both as a normal user and using run as administrator.