Your rank helps define your job and what responsibilities you have. This system also gives everybody a clear career path to follow. As you rise through the ranks, you're recognised for your hard work and you'll get a pay rise too!
In most roles, you'll join your unit as a Private. This might have a different name, depending on the Corps you join, e.g. Sapper in the Royal Engineers or Gunner in the Royal Artillery.
There are many Army roles that are only open to soldiers who are already serving, for example, Snipers, Army Divers and Army Physical Training Instructors.
Your initial commission is for 12 years, but you may choose to leave during training or after at least 3 years' commissioned service. You can typically expect to reach the rank of Captain after 3 years' commissioned service.
There are some roles, which see you join at a more senior rank. These are usually professionally qualified roles, such as medical roles or lawyers.