When the cabin crew have completed all their checks (the cabin and the galley) they then tell the senior cabin crew member. When the SCCM receives all the checks she/he then tells the cabin crew to 'take their seats for take off/landing', then gives the flight crew the signal that the cabin is secure, either electronically or via a slider, depending on aircraft type. The Captain won't take off until he receives this signal.

Once the SCCM asks to cabin crew to 'take your seats for takeoff/landing', the cabin crew should sit down immediately. They should not be having a tea or still securing the galley.