The picture “Bad Solder Joints” shows 3 common issues seen when soldering.
The Top Left Joint is caused by the solder not flowing well into the joint. This is usually caused by overheating, a dirty PCB or a dirty tip. Clean the PCB and try again.
The bottom left joint shows a cold joint. This is caused by not allowing the solder to melt completely. These will cause your cicuit to fail prematurely. Apply a little more heat to the join for longer.
The bottom right join shows a “disturbed” joint. It looks quite like a cold joint and indeed the circuit will fail prematurely with this too, but it is cuase by allowing the joint to move before the solder has cooled down.