Your friend as a now MD resident can buy most long guns over the counter. Cash and carry with just his/her DL and a simple 4473.
Some dealers in the area are very apprehensive about out of state drivers licenses though, so if he/she hasn't done that, it might make things smoother.
The MD issued temporary drivers license known as the MVA "change of address card" will also be sufficient. (Some dealers might also want additional proof of residence. Utility bill, insurance card, ETC.)

Handguns other than muzzle loaded are considered "regulated" here and require a HQL. (Handgun Qualification License.)
Those are issued by the Maryland state police. Link here.

After the HQL is acquired, the buyer then has to complete a 77R application for a regulated firearm purchase. (Also done online through MD state police.)
With that completed he/she can go to any dealer in the state and find the deal they are after. The 77R expires after a while, and then has to be renewed.
Once the dealer processes the 77R, the mandatory 7 day wait starts.
Once that has elapsed, the buyer returns to the dealer and completes a 4473 for the final transfer and can take possession of the regulated item.
(Assuming all background checks pass.)

Sounds fun right?!?

There's also a list of "restricted" firearms that cannot be transferred in the state.
Link here.
As well as a list of approved handguns that can be transferred. (Known as the handgun roster.)
Link here. This is also the link the buyer would use to apply for the 77R referenced above.