For usual Linq to SQL types you’d normally build at least entity classes, which is not possible in the UiStudio directly (they could be imported via packages though).
Here is a great article from the creators of Linq to SQL that should give you a strong starting point. The logic itself is pretty simple, most of the work is building entity representations and queries themselves.
As a sidenote - have you tried using existing DB activities? For simple cases they’re usually enough.