Hi LolaLouie,
I believe air pumps are usually a small apparatus which consists of an electric motor driving a bellows or other pumping mechanism all encased in a small plastic housing (often sort of the size and even shape of a computer mouse that fits in your hand!) and it plugs into your house electricity and sits on a surface near but outside your tank. It has one or more plastic or brass nipples over which you press the end of a small clear plastic airline. You then run the airline into your tank where it is attached to any number of bubble-making devices.
The most common bubble device is an airstone which come in small 1"(2cm) or so cylinders and break up the air into many little bubbles. There are also very long versions of these which can create an upside down waterfall-like effect along one of the glass surfaces of your tank. There are many other creative devices that accept an airline and do things with bubbles inside a tank.
There are also T-connectors (for splitting one airline into two), extenders (for hooking two lengths of airline together) and even hang-on-tank-back arrays of adjustable air splitter gangs (so, e.g., you can split the pump air 5 ways and adjust the pressure individually among each of 5 lines perhaps going to different airstones and internal bubble filters.)
air pump selection considerations:
1) size (pressure capacity): they come in increasingly expensive and higher air pressure capabilities (experience aquarists in this forum could give you good advice about this)
2) noise: Depending on your home situation, pump noise can be a big issue. Most little pumps make a quiet hum but it can get louder over time as the parts of the apparatus wear down. This is why people like to compare their experiences with different air pump manufacturers and models.
3) reliability (obvious)
(others may have more points to add to this)
There may be other community tank considerations that people can advise you about. I think air bubbles are a pretty popular and troube-free thing but who knows.. I suspect your angels were checking whether the unusual bubbles might have been food! Once they've become used to an airstone they probably won't notice it much although it is fun to watch the occasional fish take a ride up on the bubbles. Moderation is often a good starting point and it might be good to have a valve or pump motor adjustment that will allow you to limit the vigorousness of the bubbles - perhaps so your plants won't be too disturbed or so you won't get too much surface spray leading to hard water deposits on your over-tank lights and equipment.
I'm just a newbie so take all this with a grain of salt but those are my thoughts on air pumps since I happened to be online right after you asked! ~~waterdrop~~
