The first thing you should do is select what type of gun ou want a shotgun a rifle or handgun.
shotguns have many uses from brid hunting to large game or even lock picking, rifles are mainly for long range engagements and put a ingle bullet in one spot at a precise level. handguns are for self defense mainly and can easily be concealed with the legal permits.
if you choose a shotgun you should next select the action type, the main ones are semi auto break open single shots or double barrels pump action and bolt action.
pump actions are very very reliable and are pretty cheap they will cycle about anything you put in them and will function in very harsh conditions and had many mods for them.
single shots over unders or the classic double barrel are the most reliable and simplest to own and are about middle of the road in cost to very expensive they will have either one shot or two shots so not a goo idea for home defense they are good for bird hunting or clay shooting
semi autos are very costly and are very finicky with ammo. they can fire with each pull of the trigger though.
bolt action shotguns are not very common but they are reliable and can come with detachable boxmagazines for fast reoading
if you choose a rifle you have to now pick an action type. common actions are lever single shot semi auto break open bolt action and rare pump actions.
a lever action is a type cowboy gun, they usually come in pistol or straigh neck cartridges and have high capacity around 8 - 12 rounds they are fairly reliable and are usually mid to high in price.
single shot rifles are very reliable and tend to be midly expenive and you can only shoot one before reloading the gun
semi auto rifles are gun that shoot with each trigger pull until the mag is empty and self cycle, they can be cheap to very expensive
bolt action rifles are the accurate bunsh usally and are quite reliable and can be found for cheap the very very fine quality
pump action rifles are very rare and costly but are faily reliable