score:4
You'll need a Standard Visitor visa. It is issued for 6 months and is multi-entry, so technically you'll be able to visit UK few times more. The official application portal is here: https://www.gov.uk/apply-uk-visa though the process may appear confusing to some extent. When you arrive at a consulate (or wherever is your nearest point of applying for UK visas — there's a list on that site, they will ask you to pick the least inconvenient point and time), give them the invitation letter from that company, all your docs and anything required on that site.
Upvote:6
The employing company will tell you everything you need to know, and they will pay all fees. If they fail to do that then this is likely to be a scam.
Make sure that the company is on the UK government list of approved visa sponsors otherwise, again, it's a scam.
https://www.gov.uk/government/publications/register-of-licensed-sponsors-workers