Access has three parts.
Fields
A grid of fields against roles. For each, choose Hide, See or Edit. The grid scrolls sideways with the field names held still, so even dozens of roles stay manageable.
Scope
For each restricted list or tree field, choose which values each role covers. For a tree, grant this item only, or this item and below (including branches added later). A role with no grants on a field isn't limited by it.
Explain
Pick a role and an item, and Explain tells you exactly what that role can see and do with it, and why. Use it whenever someone says "I can't see it".