To get a UK entry visa you need to fill in an application.
If you have a valid passport (biometrical or otherwise) or an out-of-date passport with an official stamp of prolongation, you can apply and if your visa is granted you'll receive a confirmation by email. You can use it to enter the United Kingdom.
If you only have an internal passport or ID card, you will have to get to a UK visa centre to submit your biometric information and then once again to obtain a visa stamp in your passport. UK visa centres in Ukraine are currently closed. You will need to get to another country and apply from there.
On arrival in the UK, you must present your visa decision email or passport stamp to an officer at the passport control. They will stamp your passport with a 6-month validity period. This stamp is proof of your right to work, study and receive benefits in the UK. To extend your visa status for up to 3 years, you need to obtain a Biometric Residence Permit (BRP).
What rights do I have with this visa? Is it the same as asylum?
Unlike an asylum seeker/refugee you will have the right to work in the UK and enjoy all the same rights and responsibilities as a British citizen, apart from the right to vote and be elected. You will have the right to work and benefits, access to healthcare with the national health service (NHS) and you can study at schools or universities same as British citizens.
The visa is valid for three years and you will be able to leave the UK and return on the same basis as people with other types of visas.
If I entered the UK with an internal passport, can I leave the UK and return?
If you need to leave the UK for a while and come back, the best way to go is to obtain biometric travel passport in the Ukrainian embassy/consulate, although this can take months.
If I was refused a visa, can I reapply?
Yes you can. Please be advised that you are required to put this information in your application. Don't be discouraged however: if your circumstances have changed, your visa application can be accepted even if you had been refused before.
More information in the document here: https://bit.ly/ua-uk-faq.