When you start up Pokemon Go, you will be asked to sign in with either your google account or a Pokemon Trainer Club Account. If you are planning on playing this game very much at all, or playing long term, it will be worth it to sign up for the Trainer Club account.
You can also choose to opt-in to the newsletter, which you may want to do, as it sometimes contains bonus codes you can redeem for in-game purchases.
After the initial meet up with Professor Willow, you will get to choose a trainer that you can then customize. You will then be set up with a starter Pokemon and will become familiar with a handful of game options at this time.
Step 2 : Catching Them