This is a standard and well-known sentence that ministers or judges use at a wedding ceremony. They ask this question to each of the people who are getting married, and each one is supposed to answer "I do." By answering "I do", they are making an official promise to their husband or wife.

These official promises are called "vows". Couples can choose to use a slightly different format for their vows. Some other common phrases that you can include are:

Do you take this man to be your lawfully wedded husband, to have and to hold...

...to honor and obey...

...for as long as you both shall live?

Some couples even write their own personal vows to each other. But a lot of couples still choose the traditional version above.