A recruitment agency is a great way to discover potential job positions that you may not be advertised elsewhere. Most recruitment agencies have a large number of job positions available and some companies chose to only advertise their vacancy with a particular agency
Many agencies do not charge you to register with them but may take a percentage of your salary as soon as they find you work. Other agencies charge the employer (this is often for long term positions).
A recruitment agency can not only help you find a job but many also offer help with CV and cover letter writing, interview techniques and will even stay in touch with you through the initial start of your employment should you have any concerns or queries that you wish to discuss with them.
You can often register with a number of recruitment agencies at any time to give you a wider scope of jobs to apply for.