Your player Cole Dunlap looks incredible with that potential. I don't know his starting skills but you could definitely sell him for a nice chunk of cash if you don't want to train him.
Read the info on training that khenry gave you and you'll get a basic feel for it. Essentially you want the players that you're training to get 48+ minutes each week at the position that you're training (i.e. Pressure for PG, you need to get your guys 48mins at the PG position). You can have 3 games per week if you schedule a scrimmage, so most people focus on 2 or 3 trainees. Every Friday training for the week completes and your guys will improve in the skill that you trained.
I think you're going to drop down a division next season but you have the second pick in our draft so hopefully you can pick up a good player.