Mini Electric Airsoft Guns are smaller version of their larger sister rifles. They use 4 AA batteries and shoot at low FPS. It's a great toy gun to start with that is an entry or gateway model for younger airsoft players. They are fully automatic, do not need to be charged or cocked and shoot in full automatic.
Spring Airsoft Guns are perfect first airsoft guns for younger users that are looking for safe, but good fun. Spring airsoft guns need to be charged or cocked prior to each shot, it's a one charge, one shot. These can be fired indoors with relative safety and is a great start airsoft gun to understand operations and methods behind airsoft. Spring airsoft guns very rarely have failure or issues due to mechanical issues. And are very reliable guns to start with.
Spring airsoft rifles are the next step up from spring airsoft pistols. They are a little more powerful and have a larger shooting range than spring airsoft pistols. The more powerful Spring Airsoft Rifles, can utilized 0.2g BB's for further shooting distances and accuracy. Spring airsoft guns very rarely have failure or issues due to mechanical issues. And are very reliable guns to start with.
Gas Airsoft guns are the funnest of airsoft guns. Some employ a blowback feature that is similar to the recoil of a real gun. These only require a single charge of green gas (freon HFC 22a or propane). These airsoft guns utilize the gas to propel the BB out while pushing the slide back for a very realistic imitation of a firearm. These gas airsoft guns fire in either semi automatic (1 trigger pull, 1 shot), or some incorporate a full auto feature (1 trigger pull, many shots).
Electric Airsoft guns are the most diverse categories of airsoft. Entry level models are similar to mini airsoft, but full sized versions. Middle level electric airsoft guns are good starting guns for full sized, high powered airsoft guns. These guns have great power and have a very high performance to value ratio, making them very popular with the casual airsoft weekend warrior. Last, but not least, is the high end Electric Airsoft Guns by manufacturers such as ICS, G&G, Systema, Deep Fire, CA, VFC. These are high powered electric airsoft guns on the higher end of the price range.