Demonstrates how to enter a ship (5)
I believe the answer is:
shows
'demonstrates' is the definition.
('show' can be a synonym of 'demonstrate')
'how to enter a ship' is the wordplay.
'to enter' indicates putting letters inside.
'a ship' becomes 'ss'.
'how' inserted within 'ss' is 'SHOWS'.
(Other definitions for shows that I've seen before include "Exhibitions" , "Turns up" , "Demonstrates the musicals?" , "Exhibits" , "Demonstrates, provides the evidence" .)