A work permit is an authorisation to work in the country of destination. It is your permission to work. This is important because some visas allow the individual to enter the country but the not the right to work. In the Middle East, this is the equivalent of an Iqama issued in the form of an ID card that you always need to carry with you.
Just like the other documents, there is a fee in applying for work permit. Check with the recruiter how much is the cost and whether it is you or the employer/recruiter who will pay for it. To verify, the MRC or the government will be able to help you. Generally, the recruiter is also responsible in applying for your work permit and the costs is included in the placement fee that you paid to the recruiter.
There are conditions attached to a work permit, one of which is because of the kafala system where you cannot change employer. Otherwise, your work permit will be cancelled.