Then hit save - save as. Save it as yourmaphere.mis and save it in your add-ons folder. Then cut and paste it into a new folder created on your desktop. All textures have to be in your map folder. You cannot go grabbing random textures from random maps. If you wanna use a map's textures, copy and paste them into your map's folder and take them from there. You also need an 800x600 image named the same thing as your map is named. You will also need a .txt name yourmapname.txt
Inside this you put your name and the map's name. This is what appears when you select a map from the map list, such as when you select bedroom it says
Title: bedroom
Author: Eric Hartman