These are the standard charges in CA DUI cases. The 23152 A VC charge accuses you of driving while impaired with alcohol and/or drugs. The 23152 B VC charge alleges that your blood alcohol content was .08 or above. If you just picked these up you have a DMV administrative hearing within 10 days. Don't skip it or forget it. It's the first step in the process so take an attorney with you.
23152 (b) VC is a per se charge, meaning, you are in violation of 23152 (b) VC if your blood or breath alcohol test reveals a result of 0.08% or more. 23152 (a) VCis a catch-all statute, meaning you can be in violation of this section if you were under the influence of alcohol or, alcohol and drugs. The difference is that you can be below a 0.08%, but still be impaired to be in violation of Vehicle Code 23152 (a). Many forensic scientists that work for the government will routinely say that you can be impaired at a 0.05%; this means that even if you are below a 0.08%, you may still be impaired according to the 23152 A VC law, meaning that the government can still charge you with a DUI.
I hope this sheds some light on the difference between the two DUI statutes under California law. Most are routinely charged with both offenses, but both must still be proven by proof beyond a reasonable doubt for one to be quilty of the offense.
Just to add to the what the other attorneys have said. These charges are very similar but require different elements to prove. Just because you are over a .08 bac does not automatically mean that you are impaired. They both have the same consequences. One is not necessarily worst then the other.
If this is a drug charge then there would be no B count.