Bad co,
The Boom Vang is one of several fine trim lines that controls the shape of the sail. Sail shape is not critical for a beginning sailor, as you have found.
A flat, tight sail can de-power the rig in strong winds. A loose, billowy sail can add power in light winds.
Start reading the "Sail Trim with Don Guillette" forum when you are ready to learn more.
The boom vang can cause problems when raising the main, or trying to raise the boom with the topping lift. One thing you can start doing is to release the boom vang tension when raising the main. Snug it up again when you are set on your first tack.