If you turned your bathroom tap on this is like putting a resistor across a voltage supply. Water flows and so does electric current. If you also turned your kitchen tap on more water flows and the same for current.
In other words the "resistance" to the pressure has lowered when you add parallel paths that the water/current can take.
Eventually, after turning on more taps you notice that the water pressure has fallen and this is the same for electricity. Voltage sources, like sources of water pressure (or air pressure) can appear to remain at the same pressure even when there is a leak. A resistor on it's own (just like a small tap) will allow current/water to flow and the drop in voltage/pressure might be very small.
As more and more flow is allowed the "source" (i.e. voltage, pressure) will start to reduce just like on a battery or in your household water supply.
what's the point of resistors if there's 4 of them in a ciruit with
50volts, it won't affect the voltage.
A lot of time it's convenient to put more than 1 resistor in parallel because of power/heat dissipation. Yes, you could buy a bigger resistor but there are a finite number of packages that they come in and 1 big resistor might not suit the geometry of where you can fit 2 or more smaller resistors.
A resistor has a voltage across it and a flow of current through it - this generates heat and the power behind the heat is quite literally volts x amps. The same with a water tap but you don't notice the heat build up because water is a good conductor of heat and it all gets whisked away.
If you have a compressor for inflating tyres (for instance) have you ever noticed that the tyre valve can get a little warm after the tyre is pumped up? It's the same principle.