After you have submitted your a level results (or equivalence), and the results are good enough/ better than you offer, then you will get the offer.
Unconditional offer mean an offer when you don't need to show off your results.
Ielts and deposit are after you get the offer.
Basically, and offer is the 'deal' between u and uni. Once you get the result, you win the deal (aka got into uni). After that, Ielts and deposit are like 'negotiation' between u and your uni.