Mr. Bennet anticipates Collins visit because of the letter he has received from his cousin. Having no male heirs, the law of England ("entailment") decreed that the estate of the patriarch could not be bequeathed to female children; instead, it would have to go to the closest male relation, in this case Mr. Collins.
In the letter, Collins renounces his claim to the estate. He has been recently ordained and made the parson for the regions belonging to Lady Catherine de Bourgh. Collins writes:
As a clergyman, moreover, I feel it my duty to promote and establish the blessing of peace in all families within the reach of my influence; and on these grounds I flatter myself that my present overtures of good-will are highly commendable, and that the circumstance of my being next in the entail of Longbourn estate will be kindly overlooked on your side, and not lead you to reject the offered olive branch (Vol I, XIII).
Having a parsonship, Collins has no need of Longbourn. Called an "avowson," a position, like the one Lady Catherine offered Collins, was held for life unless he was to resign it or be found completely incompetent.
Understand that Collins would not give up the property, but neither would he turn the girls out as he would have an estate of his own. This is the reason for Mr. Bennet's warm welcome: the assurance of security for his girls.
Mr. Bennett looks forward to Mr. Collins visit for several reasons. First, Mr. Bennett is always alone with just women and a male visitor is very welcome. Second, Mr. Bennett finds Mr. Collins very amusing. He is entertained by the man's lack of real intelligence and his constant groveling compliments and apologies that last for hours. Mr. Bennet generally talks very little, but during dinner he leads Collins to talk about Lady Catherine DeBourgh, his patroness. Mr. Bennet tricks Collins into admitting that he's a suck-up without Collins ever realizing what he's done. Mr. Bennett is having great fun!
After dinner Collins tries to entertain the family by reading aloud, but the book he reads from is boring and Lydia interrupts him to talk about the soldiers who are quartered in Meryton. Snubbed by the interruption and the complete lack of interest in the book that he is reading, Mr. Collins refuses to read despite the Bennet family's polite request and apologies for interrupting. Instead, Mr. Collins plays backgammon with Mr. Bennet