You can make a polygon selection by selecting the polys and creating a polygon selection tag from the Selection menu (Set Selection). Then you can assign that selection to a texture tag by dragging and dropping the poly tag or typing the name into the texture tag’s “Selection” box.
Having said that, it sounds like the biggest issue you’re having is with UV mapping, which generally describes how textures are applied to objects. If your texture tag is set to Projection>UV Mapping then the program will apply textures based upon a flattened version of your mesh. The process of getting a good UV map can be somewhat involved. In your case you can probably avoid that by using Cylindrical projection, but you’ll have to scale and rotate the projection to get it to fit correctly.
I’d suggest you read the help docs on UV projection.