Once you have an offer of employment, your new employer will request and then issue you with a ‘certificate of sponsorship’ (COS).
The COS does not confirm that you meet all the visa eligibility requirements.
It only confirms that the job that you have been offered meets the requirements.
The certificate of sponsorship is not an actual physical document. Instead, you will receive a reference number, which you will need when you make your visa application.
Once you receive your Certificate of Sponsorship reference number, YOU must apply for your visa before you leave your country.
Your new employer can view your immigration status on-line. You will need to provide them with a “share code” to enable them to do this.
You cannot work in the UK before your visa is cleared and issued.