I am cramming to learn this by tomorrow for an interview. I've been at it since Thurs and I know I'm missing a important step but can't find the answer to it. I am building my database and I can't figure out how to link them in relationships. It keeps coming up blank..nothing in the relationship box.

I open up 2 out of the 3 databases and they have the little + in the corner and I click on it and it shows me another database....