Your plan is the part of a subscription that decides what you can do. Where a license is about a single screen, your plan is about your whole workspace: the features you have to work with, and what each license costs.
What the plan decides
Some of those features are about the screens themselves, what each one is able to do. Others live at the workspace level, shaping what your whole workspace can do. The plan you are on decides which you get.
Which features each plan includes is laid out in full in the comparison table on the pricing page.
One plan for the workspace
A plan is chosen for the workspace as a whole, not screen by screen. Every license in a workspace sits on the same plan, so you cannot mix licenses from different plans side by side. Pick a plan, and every screen in the workspace runs on it.
Plan and count together
Two things shape your subscription: the plan, which sets the features and what each license costs, and the number of screens, which is how many licenses you hold. The plan is the tier; the count is how many of them.
The rest of these pages are about that second part, the licenses behind your screens.