Each Workspace is its own copy of the Site. Use one per change, so a half-finished redesign doesn't hold up a quick fix.
hm workspace create redesign
hm workspace create fix-typo
hm workspace list
Choose what Preview shows
Preview shows one Workspace at a time:
hm preview select fix-typo
hm preview show
Publish puts whatever Preview shows onto Live.
Choose what you're editing
hm workspace select redesign
This only changes which Workspace your commands edit. It doesn't change Preview.
Tidy up
hm workspace delete redesign
Its history is kept. Publishing deletes the published Workspace for you.
Good to know
Every Workspace starts as a copy of Live. After publishing one, others may be out of date. Ask your agent to bring them up to date before you publish them.