Largely speaking I agree with what's been recommended above - But, You need to find out why the level has dropped. Modern cooling systems are sealed with expansion tanks so shouldn't really loose any coolant at all if working properly. Don't ignore it because lack of coolant, as I'm sure you'll know, can lead to overheating and if there's one thing these, otherwise robust, wee engines don't like it's overheating. They are likely to "reward" you with a blown head gasket. Apart from the usual radiator and hose checks, it's worth knowing the metal coolant pipe that runs horizontally along the front of the engine behind the exhaust manifold/downpipe is prone to corrode.
If there are no obvious leaks visible then get it pressure tested - almost any garage will be able to do this, although my choice would be a Fiat independent because they will know the potential weak points to look for. My personal preference would be to flush the system and refill with an OAT coolant, as Charlie has done, which has measurable advantages compared to the old silicate based, typically blue in colour, coolants. Probably at the age your vehicle is, it would benefit from a good flush and coolant change anyway. This is a simple procedure and shouldn't actually cost all that much, but get the leak, if there is one, checked first.
Good luck!