Once you've chosen your template by clicking "Start with [template name]" you'll set up your Squarespace account. If you're brand new to Squarespace you'll get a 14 day free trial. If you've tried it before, it might be worth starting afresh with another email address to make sure you get that 14 days free again!
As you near the end of your free trial you should receive an email from Squarespace asking if you want to extend it and if you want to, you can get an extra 7 days.
If you choose to work with a member of Squarespace Circle to design your website, you'll get a 6 month free trial.
Once your account is all set up you'll be ready to have a look around Squarespace and start having a play! I really do recommend that you take some time find your way around so that you start to find out how easy Squarespace is to use.