What a session is
A session is the running, secure environment where your tools execute. Here is what it is and how it relates to a workspace.
A session is a live, secure environment you open inside a workspace, where your tools actually run - on the platform's infrastructure, never on your own computer.
What a session is
A session is your live working environment inside a workspace. You open one in the browser, and the tools you launch run inside it - on the platform's computers, working on the workspace's data.
Think of it as sitting down at a desk in a secure room. The room is the workspace; the desk is yours for as long as you need it.
Sessions vs workspaces
A workspace is the project: its data, its people, its permissions. It lasts as long as the project does.
A session is where you actually work, opened inside a workspace. It is meant to be temporary - you open one, do some work, and close it. One workspace has many sessions over its life, and closing a session does not touch the workspace or anything saved in it.
A session starts empty
This surprises people the first time. Opening a session does not give you a pre-loaded set of tools - it gives you an empty environment. You then launch whatever the work needs from the App Store, and each tool opens as a window in your browser.
You can add tools as you go rather than deciding everything up front, and you can run several at once - a notebook alongside a code editor, for example.
Working alongside colleagues
Several people on the same project can each open their own session in the same workspace, at the same time. Each session is separate - your tools and your windows are yours - but the workspace's storage is shared.
So a file one person saves into the workspace is visible to the others. That is the point of a collaborative workspace, and it is worth remembering before writing into a shared folder.
Everything stays contained
All computation happens inside the secure environment. The tools run on the platform, not on your computer, and what you see in the browser is the tool's display streamed to you - not the data itself arriving on your machine.
Nothing is installed locally, nothing is downloaded while you work, and every consequential action is logged. Results leave only through controlled export.