May be teaching you to suck eggs, but here goes (assuming you're right handed)
Face the mag towards you clear side facing
With the lug at 1~2 o' clock rotate the clear housing anti-clockwise until it stops

You should have a hole in the clear perspex lined up through to the back of the mag

Place finger over the back of the mag opening and drop first pellet in

Wind the clear plastic face back clockwise one hole at a time dropping a pellet in each chamber

You should end up back with the 'ear' lined uo and a working mag