Hi,
What the above poster stated is correct. That link brings you to the website to create your account for the game.
If you don't want to login w a Gmail account, you create a trainer account as the developers call it.
You can also do this via the app for your device.
The game runs on wifi and cellular networks so you would need a compatible device.
Once you set up your account you will be asked to chose which team you want to be a part of. There are three teams to chose from. This applies for when you eventually want to battle other players to take over gyms. I started out playing just to grab unique Pokemon that will show up around your neighborhood and to collect items at places called pokestops. Eventually, as your level increases your characters become more powerful. For instance, I'm currently at level 21. You start off on level 1 and work your way up.
Note it will drain your battery and possibly make your phone overheat, causing it to shut down for a bit but not to worry.
Finally invest in a portable battery or a Mophie case.
As always ask questions if you have them and the mobile nations community is more then willing to help.