Go to Rufus Cook's profile. Click on "Edit"; on the right side, it says
Father, Mother, Siblings, Spouses. For Rufus, you will add a spouse, along with a date of marriage and location. It will help if you know her date of birth, parents names, etc. in case you need to create a new profile.
Be sure to copy and past your source, as well. But you knew that, right?
Good luck!