You need a Mapbox access token to use any of Mapbox's tools, APIs, or SDKs. Mapbox uses access tokens to associate your account with your requests to Mapbox API resources. You can find all your access tokens, create new ones, or delete existing ones on your Access tokens page. You can also use the Mapbox Tokens API to programmatically create, update, and delete access tokens.
Access tokens have token scopes that grant access to different actions. Token scopes define which Mapbox APIs can be accessed by a token, as well as which methods can be used to access those APIs. Access tokens have either public or secret scopes.
Your account will always have at least one public access token. This token is your default public token. When you're logged into your account, this token will automatically be embedded in example code on Mapbox.com.
Here's what an access token looks like in a Mapbox API request (specifically, the Geocoding API):