Let us crudely imagine the voltage source as a pump pumping water up to the top of a water slide, and the resistor as the slide itself with water flowing down through it.
The height difference between the top of the slide and the bottom of the slide is the same as the height difference between the top of the pump and the bottom of the pump.
The voltage source is adding energy to the system the same way the pump is adding energy to the water, that energy is used up as it flows through the resistor or down the slide.
The water must travel in a closed loop up the pump and down the slide and back to the start up the pump, if it doesn't you will eventually run out of water at the bottom of the pump. Similarly the current must flow "up" the voltage source and "down" the resistor so it forms a closed loop.
Now lets apply Kirchhoff's circuit laws to the slide analogy.
Kirchhoff's Current Law states that all of the "water" flowing into one point must flow out again:
So the amount of water entering the pump at the bottom is equal to the amount of water leaving it at the top.
And the amount of water that enters the slide at the top is the amount that leaves at the bottom.
Kirchhoff's Voltage Law states that if you follow a loop in a mesh the total voltage drop will sum up to zero.
There is only one loop that the water can take, up the pump and down the slide and back to the start, and what this law states is that if you add the height the water travels up the pump and subtract the height the water drops down the slide and get back to the start then this will add to zero.
Which is completely obvious in the slide case since if you travel in a loop back to where you started from the obviously if you are back at the start then at the end you are zero meters above or below where you started from.