ucas tariff points

hey...
Ive applied to ucas... for the 6 unis of nottingham, leeds, birmingham, manchester, kings and sussex (in no particular order) to study geography BA.

I did not receive that amazing AS grades - 2 B (geo and politics) and 1C (french), and 1D (economics).

My GCSE were fab though!

Today i got my first offer from sussex for geography: BBB or 300 tariff points.
Does that mean that you can get ABC to get a place too?
How does this tariff points system work and is it flexible?

I would be grateful to hear an answer to this.

Kind regards x