Generally, you will be on bail until your "mention day" and bail will be extended on this day so don't fail to appear! If you do fail to appear, not only might you be convicted in your absence, your failing to appear will jeopardise your chances of getting bail in future. You are also liable to immediate arrest for the offence of breach of bail. On the other hand, your appearing in court to "meet bail" can be used in your favour, in future bail applications.
Some charges are issued by way of a summons; if you are not on bail, you may not need to appear in court if your case is going to be adjourned.
Minor offences may be dealt with on any mention date where a guilty plea is entered but never plead guilty without considered and independent advice! If you are asked to plead, and plead not guilty, a date for the hearing will be arranged (the hearing may not be listed for months, even years in some cases). It is possible to change a plea of not guilty to guilty, later on; however, to change from guilty to not guilty (especially after sentencing) is almost impossible.
In a criminal hearing or trial, it is always up to the prosecution to prove the offence, and this must be proved to a standard called "beyond reasonable doubt". If a magistrate (or a jury in more serious cases) is convinced by you or your lawyer that a reasonable doubt regarding your guilt exists they will find you not guilty. In some cases there is a partially reversed onus of proof. For instance, if marijuana is found in your car or your bedroom, you must prove (but only on the "balance of probabilities") that you did not know it was there; otherwise it is legally assumed to be yours.
The central issue in a criminal trial is always whether or not the prosecution has proved its case beyond reasonable doubt. No-one has to prove their innocence. However, once a person has been found not guilty, the law presumes that person to be innocent, on the basis that all people who are not proven guilty must be presumed innocent. This principle is not always respected by police and the media, but it is the law and a fundamental right. If a person is found not guilty, he or she is free to leave the court unless they are in custody for other charges which have not been resolved.