Being on the register means an employer can sponsor workers. It doesn't mean they have vacancies or will sponsor every role. Check the job is eligible on GOV.UK, and never pay an employer or agent for sponsorship.
Registered office addresses come from Companies House and may be an accountant or head office rather than the workplace. The links search the web for each employer: check you have the right organisation before you contact them. Sector and council are worked out from Companies House records and the register's town, so a small share may be missing or wrong. Charities, NHS bodies, universities and councils are often not on Companies House and may show “Not known”. How this data is put together.