However, it's crucial to understand: You should *never* just pour antifreeze directly into the reservoir if the engine is hot. Doing so can cause serious injury from scalding steam or coolant. Always let the engine cool completely before adding coolant.
If you're unsure of its location, consult your owner's manual. A quick online search for "2001 Chevy Malibu coolant reservoir location" with images will also likely show you exactly where it is.