A person who commits a crime must usually have to face the music. In some cases, the person who commits the crime finds people who are willing to help him or her out after the crime. This can become a criminal matter for the person who gives that assistance.
When you are pulled over because a law enforcement officer has reason to believe that you are driving after drinking, things usually move pretty quickly. At some point during the stop, you might be asked to take a field sobriety test. You might also be asked to take a breath test to determine your blood alcohol concentration. You have the right to refuse that breath test, but that refusal can trigger a different chain of events.