@Nard75
You choose five now (closing date for making these choices is in Jan unless your DC is doing medicine / dentistry / vet / oxbridge, in which case it's in about 10 days).
Actually I say you choose five now but you don't have to make your choices all at the same time. You could apply to three places now and then add another two later if you wanted. Same closing date would apply though.
Then the unis you've applied to will either make you an offer or reject. This can happen at any point between now and well into next year.
Once all the unis have decided (or you can do it earlier if you want), you choose one firm and one insurance from the ones that have made you an offer.
If you make the grades for your firm choice, you are going there. If you don't make the grades you might still be going there, it's up to them whether they let you in or not.
If your grades aren't good enough for your firm and they reject you, but they're good enough for your insurance, you go there. If they're not good enough for your insurance, again, they might still let you in.
If you change your mind after you've firmed I think there's a window where you can swap firm and insurance around, but other than that if you change your mind you would have to go into clearing.
I hope that all makes sense and is accurate, someone correct me if not!