There are two different DUI charges in California - 23152(a) of the Vehicle Code [driving under the influence of alcohol and/or drugs] and 23152(b) [driving with a blood alcohol level of 0.08% or greater].
The 23152(a) charge can be for driving at any blood alcohol level if you were intoxicated by any substance and they believe the evidence shows you were unable to operate your car with the same ability as a sober person.
The 23152(b) charge makes it illegal to drive with a blood alcohol level of 0.08% or more, even with "perfect" driving. I've seen countless cases where a person is stopped for an equipment violation, NOT bad driving and they're later found to be over that magic 0.08% number.
The officer took your license, gave you a pink piece of paper. Now what?
That pink piece of paper is now your temporary driver's license. If you read the fine print, it says that your license will be suspended automatically by the DMV after 30 days unless you take action. You only have 10 days from your arrest to request a hearing to challenge this license suspension by the DMV. Miss it and your license will be suspended, no questions asked.
What if the DA doesn't file charges? Will I get my license back?
Not necessarily. The DMV goes by different standards, rules and procedures in their administrative hearings. Even if the DA's office doesn't file (or if they are just slow to file, as is often the case), it doesn't necessarily mean the DMV can't take action against your license. They're two separate proceedings and each has to be fought.
Of course, completely beating the DUI charge in court can, in some instances, undo the DMV license suspension.
I had a date to appear, but no charges were filed. Am I home free?
Not necessarily. The DA's office is notoriously backlogged with cases. On a misdemeanor (such as a basic DUI), the statute of limitations is one year. They have up to that one year to officially file charges.
If you find yourself in this limbo period, be sure to get documentation to prove you appeared in court when you promised you were going to so they can't allege a failure to appear against you.
This doesn't impact the DMV though. (see above)
Do I have to appear in court on a first time DUI?
Not necessarily. On a first time DUI, an attorney can appear on your behalf unless the judge orders you to appear for some reason. On a first time DUI, I've never seen that happen unless the case involved an injury of some sort or other serious charges being attached.