A Mapbox account can be created at the signup page.
When an account is created you can go to Tokens to see your find your Default public token. This token is needed to retreive data and maps.
To create, edit and delete styles and other data you need a secrect token.
You can create one on the Access tokens page by clicking the + Create a token button. Give it a name and check at least the STYLES scopes as shown below.
Optionally you can enter URLs to restrict the use of the token to those URLs.
Click the “Create token” to, you guessed it, create the token. After you have confirmed with your password. The token is shown on the tokens page. Pleas take note of warning and do copy the token as this is the last time it will be shown to you!
You can now add shapes of countries and other territories to your Mapbox account.