The coolant recovery tank is located in the engine compartment, typically on the fender well.
The proper coolant level is slightly above the FULL COLD marking on the recovery tank when the engine is cold. Top off the cooling system using the recovery tank and its marking as a guideline.
A coolant level that consistently drops is usually a sign of a small, hard to detect leak, although in the worst case it could be a sign of an internal engine leak. In most cases, you will be able to trace the leak to a loose fitting or damaged hose.
Evaporating ethylene glycol antifreeze will have a sweet smell and leave small, white (salt-like) deposits, which can be helpful in tracing a leak.