As of today, there are 724 different "sounds" you can listen while playing Tibia. These go from simple, short sounds such as a melee weapon's cling, to the long background tracks such as the Tibia Anthem. As you can imagine, these sounds are organized so the client knows what to play and when to play it. There are four different kind of Sound "categories", so to speak.
Sound Effects
Sound Effects consist of one or more sound files that are played by an action, creature or in the background. For example, The Sound Effect #1 is played when a character hits a creature using Fist Fighting, so it sounds like a punch. This effect has 3 different Sound files, which are very similar but still different.
The reason for 3 different files is simply to add variety. When the Sound Effect is triggered, one of the 3 files is randomly selected and played. Furthermore, Sound Effects have a range of possible pitch values, which is used to add even more variety.
The Sound Effects include battle sounds (attacking with fist or weapons, defending or taking hits), spells, using runes, creature noises (including the sound they make when they die), using items (such as foods and drinks), moving items, background noises (for example fire crackling or birds singing) and feature sounds (like Party sounds). So yeah, pretty much all of it.
Basically, these Sound Effects are all very short and usually triggered by a specific event like those mentioned above.
Ambience Sounds
We also have "background" sounds, or ambience as they are officially called. These are sounds related to the environment around the character. Ambience Sounds have two different kind of sounds:
They have one "Looping Sound", which is a constant background sound. This can be the sound of wind, sound of crickets in the jungle, sound of running water, "sound of suspense", etc.
Besides the looping sound, they are also connected to one or more Sound Effects which randomly play on top of the Looping Sound. When you're in Tiquanda, for example, you'll hear the background sound of the jungle, but also the ocasional sound of apes screaming, even if there are not creature arounds.
For this reason, there are ambiences with the same looping sound, but difference possible sound effects. There are around 80 ambiences, with as many as 7 different possible sound effects, which leads to many different possible combinations in order to, again, add more variety and make the sounds less repetitive.
Ambience Object Sounds
This small group of sounds allows specific objects in the map to emit sound for players near them. It's the sound of Fire you hear when near Lit Fire Basin or Campfire, the sound of water when you're near a river or the sea, the sound of ponds and water fonts and the sound of bubbles in the swamp.
One interesting thing about these sounds is that they can vary depending on the number of objects near you. If you're surrounded by some fire objects, you'll hear a low-pitch fire sound resembling a massive fire and not just a small bonfire.
The image above shows the Objects related to one of the Fire Ambience Object Sounds. The more of those near you, the lower the pitch of the sound will be!
Music Templates
Finally, there are Music Templates. These are the long, instrumental tracks composed for the Map Areas, as well as the Tibia Anthem and two other special tracks (one for major Boss Battles, another for the Throne Rooms).
These tracks are played when you enter the places they are connected to, but only in some conditions such as not having a battle sign. Furthermore, they don't loop continuously, having a "cooldown" before you'll listen to a track again.