I have a 68 camaro 396 big block.

How to a determine if the alternator is charging my battery?

You can get a digital multimeter from most any hardware store, Sears, Harbour Freight, Radio Shack, etc. Read directions how to use.

If you have the original design external regulated alternator, with engine running after 5-7 minutes from start-up, measure charging voltage across the battery posts, red lead on positive post, black lead on negative post. At engine idle, meter sholud indicate more than 13.2 volts. Rev up the engine and the meter should read not over 14.8 volts. This is normal.

If you have a later design internal regulated alternator, you would see the meter would indicate no less than 14.2 volts all the time. This is normal.

Both designs should have the GEN light on with the ign key in IGN, engine not running. If the GEN light is on with the engine running, there is a problem in the charging system.

Ok, I never seen the GEN light on, but I used a volt meter on the battery and showed 12.3 volts with the car running a idle, and it was the same with car off.

I went to autozon and bought a new External Regulator and installed it.
I fired it up, now the GEN light was on at idle, but goes away when u rev it. ( I checked the battery again, and its the same 12.3 Volts.)

I switched back the old regulater, and the light dosned come on, but
volts dont change any.... Any ideas?

thanks

Inside the basics sticky in electrical, there is a tech article on using voltage readings to troubleshoot the external regulator charging system.

I went to autozon and bought a new External Regulator and installed it. I fired it up, now the GEN light was on at idle, but goes away when u rev it. (I checked the battery again, and its the same 12.3 Volts.) Any ideas? thanksRegulator still needs adjusting.

Take it back and see if they will exchange it for a Wells VR715 Reg, an electronic one.

As Everett suggests..
There are 2 things to look at
1/ is the alternator charging
2/is it charging but not big enough to drive everything

Turn everything on...and at ildle the gen light should stay off...or at most a very slight glow. a slight increase in rpm above idle and the light goes off

And double check with a volt meter.

A crook battery can give false readings...get a cheap battery hydrometer and check each cell has close to the same reading...after turning lights wipers indicators on for a couple minutes without the engine going..
dont worry about if doesnt show fully charged...look for a cell that iis noticably different to the others.