How does expungment work?

I live in Maryland, and when I was 18 I received a court summons for a criminal attempted fourth degree burglary charge. I broke my neighbors screen window and never told him about it. I had to do 40 hours community service, it was a stupid thing to do but I was young and stupid lol. I am now thinking about joining the Military. My fourth degree burglary has been expunged, but does this mean I still have to document this when joining the Military? Does expungment only remove it from the public? I'm basically asking how expunging something actually does.