I think I can explain state functions.
Things that are only dependent on the current state of the system are state functions.
Gravitational potential energy is a state function.It is determined by the position of the masses in your system.(On Earth the height above the ground.)
Thermal energy is a state function . Just knowing the temperature and the specific heat capacity you can figure it out.
Enthalpy is also a state function.It is dependent on the same things thermal energy depends and additionally on the volume and pressure of the system.
You can go on like this.Entropy and stuff like the other thermodynamic potentials are also a state function
The amount of frictional energy an object "loses" to the environment between two points is not only dependent on the two points.
It is not a state function because it depends on the path.
I suspect that did not help you much, but feel free to ask it again in a more specific way.