Every model is made of faces, (4 edges, 4 vertices) really made of two triangles.
All you have to do is be able to pick out where you can make a bunch of faces together . In the example below, figure 1 has 9 vertices, and 4 faces
fiugre two shows 4 vertices, 1 face.
You can reduce it one of two ways, both have to be in edit mode.
1st would be to delete the red vertices in figure 1, and then choose the four yellow vertices in figure 1 and press the "F" key, for "make face".
The other would be to choose the four yellow vertices, press "F" for "face", and then click on the face select button while in edit mode (the triangle in the second picure) then select the four smaller faces and delete them. The extra vertices will leave as well, in most cases, and all that will be left is the one larger face.
UV mapping, I had to watch greybeards UVtutorial about 3 times, and then "play the video, and pause" twice while modelling, to ge tit figured out. He uses a complex object, which confuses things. Basically, take a box, and imagine all edges are sealed with tape. To UV map you have to determine where to make teh cuts, so teh box will "unwrap" well. In the third attachment, I marked all the edges in magenta where the "seams" or cuts would not be made. SO in the cube, the red lines would be where the "seams" or "cuts" would be made. With the "Cross shaped" uv map, you would then be able to paint each individual side. But you will really have to watch greybeards uvtutorial to understand fully.