I managed to unzip the file but when I type command sudo apt-get install it always says “command not found”. What am I missing?
Welcome to the forum! 
You’re using the wrong distribution. apt and apt-get are commands for the Debian package manager, as also used in Ubuntu, Mint, Bodhi and other Debian derivatives.
Manjaro is based upon Arch, and the package manager we use is pacman. Actually, there is also pamac, which is a different tool for installing, querying and uninstalling packages, but it uses the same package database underneath.
That said, the package format we use in Manjaro ─ and as of course also used in Arch ─ is also different. Debian and derivatives use .deb packages, while Arch and Manjaro use .pkg.tar.zst packages. Please see the relevant page at the Manjaro Wiki. 
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It appears that CLI software does not exist for IPVanish. I am not a subscriber of their service, though. It looks like you have to download their OpenVPN config file, extract and install via Network Manager.
The tutorial that they provide is a bit dated, nevertheless, it should be about the same:
Thanks I’ve been trying all day taking the wrong step
Its not normally recommended but you could try deptap. It’s a script for converting debian packages to arch. I’ve never used it myself but plenty of people have used it