Owns a company and working for an employer

How the tax calculations work, if I owns a company (doing some part time job related to my field) and full time working for an Organization. Please clarify how the tax calculations are calculated for this situation. Thank you.

Hi.
At the end of the tax year, you would file a Self Assessment tax return, declaring any income you had made through your own company.
You must also declare in this return the income you earned working for your employer, and the tax you paid on this income.
Doing so ensures you are not over or under taxed on the income you make from your own company.
You can read more here - Completing your Self Assessment tax return.
Thank you.