The end attachments just screw onto the hose - but with an anticlockwise turn
What's happening is that the hose is manufactured in very long lengths - 1000s of metres long - it's cut to size then the end pieces are attached using an anti-clockwise turn.
To attach the end piece:
Remove the end piece from the motor or from the airgun
Hold the hose in your left hand, the end piece in your right hand
Push the hose into the end piece
Turn your right hand towards you - in an anticlockwise turn
This does work, the hose is like a giant screw that screws into the end-piece.