You need to apply a texture to your terrain. By default, the texture will be all-black. The way you add a texture depends whether or not you have the public beta (caution: beta releases have bugs) as 6.31 uses a different method than 6.40.2 does.

In either version:
1. Create your texture. Textures must be a power of 2. That is, the width and height must be either 16, 32, 64, 128, 256, 512, 1024, 2048, or 4096 pixels. 256x256 is the fastest, but they don't have to be square as you can have 512x128, 2048x1024, or 32x64.

In 6.31 and earlier (your likely scenario as all-black was the default used in 6.31):
2. Access the skin edittor through the menus at the top (I don't recall which one, but I think it's the edit menu).
3. From in the skin edittor go file > import skin. If you used a TGA or PCX file instead of BMP, make sure you choose that file type from the drop down menu, find your file and double-click it to open it. Your terrain is now textured.

In 6.40.0 or later (unlikely your case as 6.4 has the option to go fully untextured, which is the default):
2. Go to edit > manage skins.
3. Click new skin, check texture, then click the texture file button, then the ... to browse for your file. Find it and double-click your file (make sure you have the correct file type from the drop down menu if you don't use the default chosen (normally BMP)). Your terrain should be textured. If it isn't, continue on.
4. Click the select all tool in face mode, return to the skin manager, choose the texture to use, then click the "set skin" button. At this point, it should definitely be textured.



As to your other question, save your file first and after saving the file, you can then add a script to your level.