Well my advice would be to start small because a game like gta is a huge load of work like scripting, modelling, level building and it will take you forever to finish it if you have the right skills. So you should start with a game like pacman or a shooter those are easy and another advice would be to do as many tutorials as you can find. They will help. For the tutorials you should look in the aums like Orange Brat already gave. Hope that helps.