Exercise your right to remain silent and ask to speak to an attorney. The worst evidence in most cases are the statements people give to the feds. Don't try to explain your actions. Don't admit to anything. Speak to an attorney ASAP
You will be brought before a judge for a bond hearing usually within 24 hours of your arrest. Bond is determined based on many factors including the strength of the governments case, ties to the community, risk of flight and danger to the community.
After an arrest the government will usually present a case to a Grand Jury. The charging document issued by the Grand Jury is called an Indictment.