It is almost always a crime to possess a firearm while under the influence of alcohol or any controlled substance. Many states also prohibit people from carrying a firearm into establishments that serve liquor (such as bars and nightclubs), even with a concealed carry permit, and even if you are not drinking.
Federal and state regulations determine how guns can be sold or transferred and who can receive them. Violations of these laws can result in criminal charges, so it's important to know the rules before selling or gifting a gun.
Privately made guns, including ghost guns and 3D guns aren't heavily regulated by the federal government, but some federal restrictions still apply. And a growing number of states have outlawed untraceable homemade guns.