What do it mean when my battery light on an my alternator an my battery good

It could mean there is too much restistance at the connections. Resistance is cause by oxidation, corrosion, improper assembly, air gap, dirt, looseness, The alternator needs to have a good path to charge up the battery as it discharges, fuses that are blown or wires with resistance at their connections can stop the process. when the voltage of the battery drops, the light comes on. A new battery can be bad, an alternator can be inadequate, the system can draw and use too much power, etc. After the connections are cleaned with a wire brush and the mess is cleaned with baking soda and water. you can get it to a place where they have a tech who can run tests and verify the parts and the connections are good, the system is within tolerance, and the engine of course must have an alternator belt and proper tension.

I had the alternator replaced and I bought a new battery

so ewhy is my battery light still on