I need to travel to London from USA, and I am a green card holder. My nationality is Albanian. Do I need a visa to enter the UK?
You can check if you need a UK visa at this gov.uk web site.
I ran through it with your citizenship, and guessed that the purpose of your visit would be tourism, and the result is that you do need a visa.
Unlike some other countries, having a US green card does not give you visa-free (or visa on arrival) entry to the UK. As noted by @MartinBonner in a comment, having a green card could improve the likelihood of your visa application being approved.