In the middle, you'll see your Buddy tap him for a yell! You will miss a lot of the Gyms and Pokéstops.
That means fire is weak against water, grass is weak against fire, water is weak against grass.
If you're already a Level 30 trainer, then you may not care about this tip.
Then go to Style to be able to change everything from your hair and skin color to your backpack and shoes.