louise, i assume yours is a thetford. there are basically two types, bench and swivel. If it looks like an ordinary loo it's a swivel. Starting with this one. Outside the van find the two doors, one above the other. Open the bottom one, that's the cassette. thsi is held in by a handle on the base. Push this up and drag the cassette out. Unsrew the yellow cap and put blue fluid in as on the bottle. Put in about 2 litres of fresh water. Close cap and put acssette back in. Lock door. Open top door. Using a funnel put pink fluid in there as on bottle. Then top up with fresh water. (takes about 10 litres I think.)
On a bech type you have one door. the pink fluid goes in the top nozzle that will swing out. The cassette is the same.
Flushing: swivel- open valve, LHS of loo, and pump hadle on cistern Close flap. bench open valve, righ hand big knob, twist, then twist left hand knob to flush.
With both we have found it bets tu use it flap closed with a small amount of pink water in at the start.
When you are happy with this come back and ask about cleaning and lubricating the seals.
Good caravanning. Don't forget to empty the cassette before towing.Suggest you do this evryday on site as it gets too heavy otherwise. Don't forget to empty everything before winter, and only use Thetford plastic cleaner to claen it with.