[David G4EBT]

You peel the clear protective film off one side only initially - it doesn't matter which side you peel off.

Then you lay the unprotected side of the purple film to your PCB laminate, taking great care to exclude all air bubbles. The you put it through a laminator to seal the purple UV film to the PCB. From my experience, you need only one pass and if you end up with bubbles in the film, it doesn't solve that however many times you pass it through the heated laminator.

Assuming that there aren't any bubbles, you then put the PCB in the light box with the negative UV mask and expose it. Having done that, you peel off the upper protective film and place the exposed PCB in the developer. Check for any blemishes and touch them up with whatever - modelling paint, rub down transfers, nail varnish etc. If you're in luck, that won't be necessary.

I don't use pan-scrubs etc to clean the laminate before applying the film - I use 0000 grade wire wool, otherwise you risk creating score marks in the copper which can result in tiny cracks across tracks after etching, which are only visible with a magnifier. If you tin the board, that might bridge the cracks but it's best to not create them in the first place.

I've attached a sketch to make things a bit clearer.

Hope that helps.