This is one of the sections required by law to have in your marriage ceremony. The minimum legal wording is as follows:
“I call upon the persons here present to witness that I, [full name], take thee, [full name], to be my lawful wedded wife (or husband)”
In addition you can add traditional vows, some of which can be found here.
Finally, and perhaps most enjoyably you can write your own. Modern vows tend to come across as cheesy, writing your own on the other hand, is both earnest and beautiful. Vows are really the business part of the ceremony, you are both setting the terms of the contract that you want to live by. So it makes sense to write vows that make sense for you. Personalised vows usually contain two sets of elements: saying nice things about each other and making promises. Some examples can be found here. Some couples like to write their vows separately and only read them to their partner on the day, don’t worry, if you do this, I’ll discreetly let you know if your vows don’t quite match up and help them to be more even!