"It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife. However little known the feelings or views of such a man may be on his first entering a neighborhood, this truth is so well fixed in the minds of the surrounding families, that he is considered the rightful property of someone or other of their daughters."
Simple: Everyone knows this is true: that a man who is not married and who has much money, must want to have a wife. Even if people don't know what the man thinks when he comes into a neighborhood, this idea is stuck so firmly in the minds of the people of the neighborhood that they think he belongs to one of their daughters.
"She [Mrs. Bennet] was a woman of mean understanding, little information, and uncertain temper."
Simple: She was a woman who did not understand things well, who did not have much information, and who got angry easily.
"She is tolerable, I suppose, but not handsome enough to tempt me; I am in no humour at present to give consequence to young ladies who are slighted by other men. You had better return to your partner and enjoy her smiles, for you are wasting your time with me." (Mr Darcy to Mr. Bingley about Elizabeth Bennet)
Simple: She is okay, I guess, but not beautiful enough for me. Right now I'm not in the mood to help young ladies feel important, at least not young ladies that other men don't want. Please go back to your partner and enjoy watching her smile, because you're wasting your time talking to me.
"But I can assure you," she added, "that Lizzy does not lose much by not suiting his fancy; for he is a most disagreeable, horrid man, not at all worth pleasing. So high and so conceited that there was no enduring him! He walked here, and he walked there, fancying himself so very great! Not handsome enough to dance with! I wish you had been there, my dear, to have given him one of your set-downs. I quite detest the man." (Mrs. Bennet to Mr. Bennet about Mr. Darcy)
Simple: "But I can tell you," she added, "that it is not important that he likes Lizzy; because he is a most cross, horrible man. He is not good enough to make happy. He is so proud that I cannot bear him! I wish you had been there, my dear, to stop him from being proud. I really hate him."