If you’ve been granted a clearance and deemed need to know you’ll be given access to classified information appropriate to your level and program.
Step 1: You’ll be briefed and shown how to access your Security Classification Guide or DD Form 254. Which explains in excruciating detail exactly what is classified.
Step 2: Don’t discuss with anyone you’re not sure is authorized.
Step 3: If you’re not sure talk to the originator of the information. If you’re the president, I guarantee they’ll let you know.