The ship is anchored offshore . They use the large tenders, usually carried by the ship, but sometimes public tenders from the port are used. A stair case usually goes down one flight from a side entrance to the ship to a platrorm at water level to which the tender is tied. There can be anything from calm sea with no real issues to large swells
which can in fact hamper someone not terribly stable on their feet. At every point there will always be crew to assist you on and off , but, let me reiterate, in large swells you can have a problem getting on and off the ship.
On shore there will also be crew to assist your getting out of the tender and back on again.
If you think you have a problem, make your problem known to the officer in charge of the tender operation and he or she will get you as much assistance as you require.