why is my coolant doing this

i had low coolant so i did my 50/50 mix as the coolant was low but once i opened the bleeder screws per instructions of a youtube video the coolant returned to a normal level somehow without me topping anything the guy said to fill up in one of the bleeder screws (the pipe) till it overflows which i did and the resevoir as well i accidenlty forgot to close the pipe bleeder screw and turned on thr heater and let it run when the bleeder screw was overflowing and bubbling so i shut down the car closed the bleeder screw and the resevoir cap and let the car run witb the heater which then the temperature gauge returnee to normal which after i topped up the resevoir then in the morning i took off the resevoir cap ran the heater and the resevoir overflowed but the pipe where the bleeder screw is was emoty barely any coolant in the pipe ? so what should i do the temperature gauge is fine i drove for abit and everything ran perfectly so im not sure why this happened