Mr. Bingley has danced with and shown an interest in Jane, Mrs. Bennet's oldest daughter, at the Meryton assembly, which attracts the mother's attention. We learn that

Mr. Bingley had danced with her twice, and she had been distinguished by his sisters.

Mrs. Bennet notes to her husband that Jane is the only woman at the assembly Mr. Bingley danced with twice. This gives Mrs. Bennet hope that he might fall in love with Jane and that love might lead to marriage.

This idea appeals very much to Mrs. Bennet because Mr. Bingley is a wealthy young man who has rented Netherfield Park, a nearby estate. His entry into the neighborhood has caused a stir and is the cause of the famously ironic first line of the novel:

It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife.

Mrs. Bennet has five daughters, and the estate that supports them all will pass to a male cousin, Mr. Collins, upon Mr. Bennet's death. Since they have saved almost no money, this event will leave Mrs. Bennet and her daughters virtually destitute. Therefore, Mrs. Bennet feels under immense pressure to get her daughters married as quickly as she can to husbands with the money to support them in the style to which they are accustomed.

Mrs. Bennet's open anxiety and her blundering stratagems to try to get her daughters married are counterproductive and embarrassing to her sensible older daughters, but they reflect the lack of options for ladies of a certain class in that time period. Mrs. Bennet knows her daughters have no other viable option but to marry.