imagine an object is dipped in rubber, and your task is to make cuts in the rubber, in a way, that when you have peeled it off, it lays out somewhat flat, like a tailors pattern. where you would make those cuts is where you want to mark your seams. to mark a seam, select one or more edges, and hit ctrl E ( edge menu ), then select ‘mark seam’. once you have marked your seams, select all faces, and hit U ( unwrap ). that will bring up another menu. select " unwrap ".
Top viewport: three objects joined to one to show problem areas collectively
Outliner: showing the names of the original three
Earpiece has intersecting geometry. Baking ambient occlusion would most likely produce black areas.
Spring piece has one face rotated so that the edges intersect - this is covered with another object and those covered parts would take unnecessary space on the UV layout, if laid flat.
Front piece has intersecting geometry. Front face is moved inside. Moving it back out reveals that right and left ends don’t match. Other end has an n-gon while the other doesn’t.
Each object has n-gons (faces with more than 4 vertices). They’re quite flat (planar) so probably won’t cause much issues when unwrapping, depending on how you put your seams and how many of those are actually important. But in general it’s quite rare that you would want n-gons in a final model and they can cause issues with unwrapping.
All objects have scale of (xyz) 1,1,1 which is correct.
I’m not familiar with source engine and not going to research it. I quickly scrolled through the page though and it states that props should be around 1000 polygons (for hats). Since the context is game engine, polygons mean triangles and yours already has over twice as much.
Because it’s for a game and polygon count is so high, I would suggest to delete all faces that are inside another object or not visible otherwise. It lowers the polygon count and makes the part easier to unwrap. Most of the polygons are in the spring piece and that’s too many. Model it again (maybe also redesign) with less polygons or lower the polygon count on the existing one. Currenty it’s in two parts, make it continuous so that it doesn’t have unnecessary faces in the middle of it.
How to fix intersecting geometry? Move vertices/edges/faces so that they don’t intersect anymore.