how does supabase work

Im' really interested in using supabase but need to know how it works
like I have a REST API, a GraphQL? API.
So going for REST the isomorphic client is gonna usa fetch/xmlhttprequest?
Going for GraphQL is going to create a websocket?

When using on backend, i use a service role which is permitted for every table/row/column. Am I able to execute directly SQL Statements via a native postgres client to reduce overhead?
Realtime Subscriptions also work via Websocket?
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