From the USNA.edu website:
Candidate Visit Weekend (CVW) is a program conducted aboard USNA during the Fall and Spring academic semesters to expose candidates to all facets of life as a Midshipmen.
CVW is an opportunity to sample university-level academics at USNA, to discover whether the Naval Academy will help you achieve your goals, and to offer valuable insight into the admissions process.
CVW is offered by invitation only throughout the academic year. Invitations are largely based on the level of completion of your application.
If you received this invite, then they probably gave you the option of selecting one of two (maybe three?) "weekends". I'm putting "Weekends" in quotes, because they typically go from 1700 Thursday through 0900 Saturday. It's not so much a "weekend" as a ;
1. Get-Acquainted Thursday night thing with an informative movie and meeting the 4/C MIDN who has signed up to have you as a "drag".
2. Spending the night in the room with your assigned MIDN either on the floor or in a cot.
3. Spending all day Friday following your MIDN around to PEP, classes, sports, more classes, and having three squares in King Hall.
4. Spending the night in the room with your assigned MIDN either on the floor or in a cot.
5. Having breakfast and here's-your-hat-what's-your-hurry get the heck out of here, kid!
They typically get back to you pretty quickly after you respond to their invite, with a "you're all set, see you then!" confirmation EMail. Later, as the weekend gets closer, there will be other EMails to tell you when to plan to be there and when to plan to leave (especially important if you're flying there and back). When arranging aircraft flights, you can fly into BWI (Baltimore–Washington International Airport) or DCA (Ronald Reagan Washington National Airport), with BWI being the closest when it comes to ground transportation.
Depending upon the time of day, it can take over an hour to get to USNA from Washington DC (about 44 miles West of Annapolis), but only about 30 or 40 minutes from Baltimore (about 24 miles Northwest of Annapolis).
The reason I mention DCA is because depending upon where you're coming from, it could be cheaper or faster to get there instead of BWI. The ground transportation takes longer and costs more, so that would be something you need to factor into your travel time to and from USNA.
There are a number of ways to get back and forth. SuperShuttle is a good service. Taxi, of course. Uber or Lyft are options too.
Also keep in mind that depending on the date you select, you may be in school. This should be an excused absence (Thursday and Friday) because it should qualify as a "College Visit". Check with your High School attendance office if that's the case.
Have fun!