Peugeot 3008 water is coming out of the water bottle in the engine...the heat gauge is going up and down

Could be a sticking thermostat , check engine coolant fan is kicking in when temp rises . Worse case scenario if still having problems , carry out a block test for cyl . head gasket problems

so the first time it happened the water and coolent was overflowing from the resovoir.The cap was tight but the pressure was still pushing through,so i put in more water and drove it,,, only for 2km but i need to understand how to fix it

I have given you possible causes which need checking by someone qualified or more knowledgeable . You might be better getting a workshop manual if you intend to do any work yourself or perhaps get a garage / mechanic to look and check it out if you are not mechanically inclined .