Level 3 first aid is the most advanced form of first aid. It is also officially called Provide Advanced First Aid and includes everything from levels one and two, as well as additional training. However, you do not need to have prior level one or two certifications to be begin training for level 3 first aid. You can simply start with level 3 training.
Sometimes learning first aid is required through your job, but even if it is not necessary for employment, level 3 first aid training is an invaluable tool to have.