i watched a couple of videos and there are different recipes... 

for some reason one person used salt as a stabelizer for the eggwhites. Is that right? 

Another person adds cream of tartar which i understand but im confused about the salt... 

Also people say to bake it and leave it in the oven for about 4-6 hours preferably over night, but like the problem is my oven is faster than normal ones so ofcourse have to alter the oven time as well as the temperature and because of that i need to know if my food is done cooking whihc requires opening the oven door. but the person said to leave it in the oven and let it dry out. exactly how do i KNOW when it is ready? and can i open the oven door? 

i have another question, does it matter if i use super fine sugar or powdered sugar? because recipes use different types... 

Do you mean meringues? Sugar + egg-whites beaten until stiff and then baked in a slow oven? I've never heard them called 'meringue cookies', so I'm not sure if this is something else entirely...

This is a great recipe and the instructions are pretty much how I make them: http://www.nzwomansweekly.co.nz/food/recipes/white-meringues/

Note that 100 degrees Celcius is around 210 degrees Fahrenheit.

Caster sugar is what you would call super-fine sugar.

In the end, how long you bake them for depends on how you like your meringues (I like mine to be crunchy on the outside and marshmallow-chewy on the inside) and the size of the meringues. I'd start with the recipe linked above and then play around until you get them just as you like them. I don't think you need to leave them in the oven overnight unless you are making a pavlova (a very large meringue) or you like your meringues especially crunchy.

Yes, you can open the oven door to check them.

Thank you :) 

i appreciate it