While in the "People" view, select "Tools" and then "Relationship Calculator", shown left.
If you've already selected one of the two individuals you want to include, they should already show up when the Relationship Calculator opens. Probably, the other individual will be the home person. It doesn't really matter because you can change both individuals once in the calculator.
In this case, there was no blood relation between husband and wife but the relationship calculator is also very useful for cousin marriages and working out their degree of relation. In these cases, you will see a name or names listed under the section "Nearest common relative(s)" and around the bottom right there will be numbers for Civil Degree and Canon Degree which are the degrees of relation as defined by Civil Law and Canon Law.
By the way, the hardest thing about doing these FTM tutorials is making sure I haven't inadvertently displayed information about living people in my tree when taking the screen shots!