UV mapping is in essence a method of laying the mesh out flat in order to orient textures onto them.

The best appraoch is to mark sharp edges for simplicitys sake.

Enter edit mode (tab) and select the edges (2 for edge select) where the seams should be.

With the necessary edges selected, right click and select „mark seam“. This is where the model will be „split“ in UV space, and should be indicated by a different colour.

Press A to select everything on the object, then U and choose either „unwrap“ or „smart unwrap“. Depening on the model, one or the other will produce better results. In addition, smart unwrap allows you to set a cutoff angle for UVs- in other words, what degree of angle and edge can have before it is split on the UV map.

On the top row of tabs, select UV Editing. The left screen shows the object unwrapped and essentially laid flat.