After a successful sign-up / installation of ERPNext, on your first sign-in, you will be shown a form to fill.  This form will create your first Company and Fiscal Year (accounting or financial year) record. You can create other Companies later.
This will also set the default Currency and time zone for your account. Once your complete this, your first Company and Chart of Accounts will be created.
Congrats! You are already on your way.
The next step is to configure your Chart of Accounts or start adding users and setting their permissions.