Entry of foreigners from visa countries, who want to get a job, is limited by quotas. To ensure that a worker of this category can enter a country and start working, the employer (only legal entity) must submit an application to the migration department to issue an official guest, as well as to hold a work permit. But first the employer himself must obtain permission to recruit foreign labor within the quota.
The permit is valid for a period specified in the contract, but no more than one year, and is "tied" to a certain region. It can be extended only in case of grounds, for example, if the employer prolongs the work contract.
Moving to another region, practicing a profession other than one of that specified in the permit, cannot be realized: you need to issue a new document.