Once you place the evolution card on the basic, the pokemon loses its original attack on the basic and learns new attacks on the evolution. Plus, any ailments the pokemon once had are cured. The last type, the trainer card, is a very big help in the TCG, but is again not required. Trainer cards are played only once, and then are discarded. Trainer cards are meant to help you, as they have special effects designed to either make your opponent lose, or make you more powerful.
Trainer cards are very, very useful in many decks and they usually win the game.
Draw 7 cards from the top of your deck. Do not show them to your opponent, and put the rest of your deck face down. You and your opponent should search your 7 card draw for a basic pokemon and place it on the table as your active pokemon. If either of you don't have basic pokemon in your 7 card draw, you need to shuffle those cards back into your deck and draw again. Each time that happens, the person who didn't do this gets to draw 2 extra cards.