I assume you have registered an app at Facebook and you have your application client_id and client_secret.
Here are the steps to obtain an access token @ Facebook and how you can use it:
https://graph.facebook.com/oauth/authorize?redirect_uri={your_redirect_uri}&client_id={your_client_id}
If you are not logged in Facebook, you will be redirected to Login page at FB. Upon successful login, you will be redirected to your redirect_uri(in the first request) and a query param code in the URI
Copy that code(auth_code) - it will be used to obtain an access token.
https://graph.facebook.com/oauth/access_token?redirect_uri={your_redirect_uri}&client_id={your_client_id}&client_secret={your_client_secret}&code={auth_code}
as a response you will receive an access token
Then you can use that access token to obtain your FB profile, for instance:
GET https://graph.facebook.com/me
plus Authorization: Bearer {access_token}