Agree with the above.
Sand and gravel are both widely used and liked. Ultimately it mostly a choice of what you like. Each has its own differences in maintenance and details but either can be learned. The actual choosing of which sand to get is an area where the other members here who are local to your location may be of help and advice about general type of sand can also be a bit local. Gravel is usually obained in bags at the LFS and is more obvious. Substrate cleaning during the siphoning that occurs with the weekly water change (an essential habit!) is done with sand by opening and closing your thumb at some height above the sand such that your suction force cleans the surface debris (or there are other techniques people work out.) Gravel siphoning is done by working a large clear cylinder deep into the gravel and letting the water suction rattle the debris free from the gravel its trapped in. With sand, there will always be some lost to your backend catch bucket when siphoning but its so cheap it doesn't matter.
Water movement through filter media can be accomplished by either a water pump or an air pump. An air pump usually must force bubbles through an underwater plastic tube that is part of the filter to move the water that's between the bubbles of air out of the tube, setting up a suction and water movement through the filter media box. This air pump method is generally not able to match the flow rates that can be acheived with water pumps. The whole general use of air driven filters, while still used quite a bit by experienced aquarists, is, I believe, older historically than the use of small water pumps. Water pumps, pump heads on filter boxes, have generally become more common in mainstream tanks, whether the filter is internal, HOB or external (large sumps have generally always used water pumps.) But air driven sponge filters or simple air driven box filters are still often used by breeders or in fish-house situations where practicality outweighs aesthetics, such as breeding, grow-out, hospital or quarantine tanks.
Of course, in display tanks, air pumps also have a show aspect for creating bubble displays. Simple air lines can put bubbles through a child's decorative "diver" or other decoration, or airstones can create a surge of tiny bubbles or a long wall of bubbles. These displays are for looks and do not add significantly to the oxygen content of the water. For that function, surface agitation is much more important. Surface agitation can be acheived via filter pump output going through either a "spraybar" with several holes or via a larger single outlet pipe directed at the water surface. Disturbing the surface with air bubbles also of course can do a little surface disturbance, but not as much as a directed stream or spraybar. One other minor benefit of an airline sending bubbles up through a tank is that it can add a minor addition to lower level water circulation, though not as much as a "powerhead" that is purpose-built.
~~waterdrop~~
