1
general::
Also, have straight. Understand correctly or make something clear, as in Now let's get it straight? you'll take over at four, or Do I have it straight about when you're leaving? This expression uses straight in the sense of "in proper order" or "not confused." [c. 1920]
American Heritage Idioms
2
general::
Phrase(s): get something straight
Fig. to understand something clearly. • Now get this straight. You’re going to fail history. • Let me get this straight. I’m supposed to go there in the morning?
McGrawhill's American Idioms And Phrasal Verbs