Basically you first apply a resin coating called gelcoat to the interior of your mould and this gives your surface finish. You allow this to cure until it is tacky to the touch (about an hour), you then apply your matt and or tissue and impregnate with resin until you've reached the wall thickness your after. After that you allow it to cure thoroughly and then you can remove it from the mould.
Moulds can be fibreglass or rubber due the complexity of what your reproducing. If using fibreglass moulds there's a strict regime of waxing and polishing to ensure the part releases properly from the mould - don't do this correctly and there's a good chance your part is never coming out the mould. Silicone moulds are self releasing and don't require any release agent.
You have two choices of resin - Polyester and epoxy. Polyester is cheap and has a quicker turn round time, but it has a very strong odour and makes your working environment smell. Epoxy is slightly more expensive and has a much slower curing time, but it has very little odour.
Both require well ventilated working areas and are / can be very messy to use until you get the technique.
You definitely need good protective equipment - respirator, gloves, disposable clothing (I did say it was messy) and protect all working surfaces with polythene or paper.
Sounds complex, but like anything else it's quite straightforward with just a bit of practise.
