If you just bought your VPS, please give it 5 to 10 minutes to do an initial update and upgrade at first boot.
If you log in in the first minutes, and try to install some application, you might get an error saying the /var/apt ( or alse ) is locked. This is because there is an ongoing update and upgrade running in the background.
Depending on the VPS performance and number of files, the initial update and upgrade might take a few minutes, please be patient.