What they are. A workspace is a business: it has its own members, its own plan, and its own settings. A portfolio lives inside a workspace and holds one brand or client's connected accounts and data. A small business usually has one workspace with one portfolio. An agency or consultancy may have several portfolios in one workspace, or a separate workspace per client.
Moving between them. The portfolio name at the top left is the switcher. Open it and you'll see the current workspace's portfolios, each with its ID. The back arrow takes you up a level, to every workspace you belong to; choose one to see its portfolios. Click any portfolio to open it. OmniCommand remembers where you were and brings you back there next time you sign in.
Creating a workspace. At the foot of the workspace list, choose Create workspace and give it a name. The new workspace starts its own setup: naming it and its first portfolio, then connecting sources. How many workspaces you can own depends on your plan: the pricing page lists each plan's allowance.
Creating a portfolio. Inside a workspace, admins add portfolios in Settings, in the workspace's Portfolios section, with Add a portfolio. During early access, a workspace can have 1 portfolio.
Belonging to several. One account can belong to many workspaces: your own and ones you're invited to. Your role is set per workspace, so you can be an Admin in one and Read only in another. An account can hold access to up to 10 workspaces; if an invitation would take someone past that, it's refused until they give one up.
Portfolio-only access. A person can be invited to specific portfolios instead of the whole workspace. They see those portfolios' data, settings and people, and none of the workspace's controls: no workspace member list, no plan, no workspace settings. If the workspace is still being set up, they see a simple waiting screen until it's ready.