Creating a relationship between two entities (say, a Candidate to a Candidate Committee or a Political Committee to an Affiliate Committee) is actually quite simple.
From either entity record, go to the “Relationships” section
Click on the little green “+” sign in the upper right corner
Enter the name of the entity you want to set a relationship with in “Affiliated”
Select the type of Relationship
Click “Add Relationship”
There is no need for you to set the inverse relationship – the system will do that automatically.