This tutorial will cover the steps required to get a custom texture working in your mission. Creating textures is already discussed in this Texture Tutorial, which also discusses texture families.
To load your texture, you can either add the entire family, or add the single texture. To load the entire family (assuming the family name is Mynewfam), use the command add_family Mynewfam
To load just a single texture from Mynewfam (assuiming it’s called Mytex), use the command load_a_texture Mynewfam Mytex
In the white status bar at the bottom of the Dromed window, it should then say Added Family or Loaded single texture.
Don’t be tempted to compress your texture palette just yet. It won’t do any harm if you do, it’s just a precaution in case you accidentally save and reload your mission without saving the gamesys. In such a case, the textures would end up in the Missing section of the Object Hierarchy and you’d then have to move them back to the correct place.
Open the Object Hierarchy, and select Textures from the Show Tree menu at the top:
At the bottom you can see the newly added texture. Above you can see existing material groups. Select your texture, then hold down the left mouse button and drag the cursor onto the desired material. As you drag, the cursor should turn into a + shape. When the correct material is highlighted, release the mouse button:
The texture will then disappear from the current window. Open up MetalTex and you should see your texture at the bottom of the subtree:
This is the part that confuses a lot of people. The Textures Tree is stored in a .gam file (a.k.a. the gamesys). By default all missions use dark.gam, but once you start making changes it is very sensible to use a new gamesys and leave the original intact.
There are two things to do:
From the File menu, select Save Gamesys. The new filename is up to you, but it is recommended that it’s not too similar to the name of the .mis file, otherwise the you could easily get the two confused. That would be very bad. Save the file into the same folder as Dromed.exe. Once the gamesys has been successfully save, the status bar should look like this:

On the left is the most recently saved file, and the next item is the currently associated gamesys.
Even if your mission already uses a custom gamesys, it is best to save as a new gamesys anyway, because then you’ll have a working backup.
In the command box, type the command set_gamesys custom.gam (replace custom.gam with your own gamesys name). The status bar should then read:

Now all you need to do is save the .mis file, so from the File menu, select Save Mission. It is best to save it as a new .mis file and so that you can use the previous one if things go wrong. After that, the status bar should then read:

To ensure that everything has worked, reload the mission. You can then go into Game Mode and ensure that the texture(s) make the correct sounds.