Adding Coolant
 

Does it matter what kind of coolant to add as long as its mixed?
My Coolant level is right below then"low" line (when the car is cold)
I don't know If that's ok or not since it expands when it's hot?

How far below and when was the last time you had it filled?
Generally coolant level should not drop, but top up 1 liter in a year should be ok if you live in hot climate.
If you consume a liter in a month then there is something wrong, maybe a leak somewhere.
I would suggest to bring it to dealer.

Mine drops almost half way between the 'full' line and 'low' when cold. If it's below the 'low' line when cold I'd have it checked just incase.

for our cars i would suggest going with what is recommended from the factory and that is the blue coolant. the blue coolant comes pre-diluted so you dont have to add water, just top it off.

Just a little below the low line
I've never added any since I've had it for 7 months now when it was full
When I went in for my first oil change I pointed it out to them
But they didn't top it off and marked it as ok so I don't know
It's just bothering me :(

Nah, I think you should be ok. When you see it after you drive the level will be between the low and full.

Just find the correct coolant, top it up a bit and monitor it.
I had a car with bad head gasket before and the car took a liter of coolant every month.

It's a good idea to check your fluids (oil, brake, coolant) every 2 weeks or at least once a month.

If it's getting worse mention it to dealer when you do the next service. Ask them to do the compression test or sniff test.