Oh and as for the format it's easy really
Each week there's a Head of Household competition (this varies between a quiz, a physical challenge and an endurance challenge), the winner is named the HoH and must nominate two houseguests for eviction.
There is then what's called a Power of Veto competition in which the two nominees, the HoH and three other players selected by random draw compete to win the Veto which gives the holder the opportunity to save one of the nominees (if the nominees win they can use it on themselves). Whoever wins the PoV can either save a nominee or leave the nominations the same. If the Veto is used then the HoH must name a replacement nominee.
After this the nominees are locked and on eviction night every houseguest other than the two nominees and the Head of Household goes into the Diary Room and vote to evict one of the nominees. Whoever has the most votes is evicted, and in the event of a tie the HoH casts the deciding vote.
Once there are nine houseguests left, every person evicted from that point on becomes a member of the Big Brother Jury (made up of seven houseguests, though in BB15 it was 9), is sent to a remote location and sequestered in what's called the 'Jury House' (like a posh mansion in Mexico or something) and on finale night they return and each cast a vote for one of the final two to win the show. Whoever wins wins $500k and the runner up gets $50k.
The nomination and voting process are naturally open to discussion and most of the episodes focus around strategising, but there are some bits where romances/friendships are given airtime.
Oh and also there's a Have/Have Not competition every week (previously just a food competition), two teams compete for privileges and the losers become 'Have Nots' and have to sleep in an uncomfortable room and eat 'slop' (this disgusting looking rice pudding kinda thing, it's weird) for the week. In earlier seasons though it was peanut butter and jelly, but you get the gist.
Hope that clears everything up for you, and enjoy whatever season you choose to watch

it's a much better format than BBUK in my opinion