Vias connect the top surface of the board to the bottom (considering only a two-sided board).
Uses include:
1) Routing a connection that needs to change sides, e.g., to cross over another connection;
2) Connection to a ground/power/ or signal copper pour;
3) Components on both sides;
4) A mixture of through-hole and SMD components; and
5) Conducting heat from one side to the other.
View them as similar to a through-hold plated pad, but generally smaller.
Vias connect the top surface of the board to the bottom (considering only a two-sided board).
View them as similar to a through-hold plated pad, but generally smaller.
Note that the connections (routes) change from bottom to top. Consider this, you have a TH capacitor mounted on top. Soldering on the top is difficult (but can be done). It is easier to solder on the bottom, then bring those connections to the top for soldering to C3, which is an SMD. That is my point #4. The other via allows the two tracts to cross from the capacitor to Pin2 over Pin1 to the SMD.
Those are the only vias I see in that design. The other green things are plated through holes for the TH components or mounting holes.
I have circled two of them:
Those are the only vias I see in that design. The other green things are plated through holes for the TH components or mounting holes.
It's hard to comment as the routing is pretty straight forward. It could be made smaller, but that may not be what you want to do. Do you want the LED on the backside (it's mirrored)? Of course, since it is just two pins, it can go on either side, but the silkscreen will be on the back. Even though 24 mil might be a good minimum for route width, I would still go thicker as in the example you posted (Post #3).