Firstly, an employer needs to hold a sponsor licence with UK Visas & Immigration. This requires them to go through the application process so that UKVI is satisfied that it is a genuine organisation operating lawfully in the UK and has the procedures and processes in place to take responsibility for workers that are sponsored.
Once a suitable candidate is identified the employer will need to obtain a Certificate of Sponsorship (CoS) and assign this to the prospective employee.
Once the individual has the CoS, they will then be able to apply for their visa to work in the UK using their assigned CoS.