Zip is a compression method and utility program in Linux. You can compress single files and folders with it. This tutorial is about to zip a single file. To zip an entire folder, check article Create Zip File From Folder Recursively in Linux.
Let’s assume that your file is name myfile.txt. In Linux terminal, type:
$ zip myfile.zip myfile.txt
This will create a zip file myfile.zip in the same folder.
You can also add multiple files to the same zip file:
$ zip myfile.zip myfile.txt another.txt another2.txt
To see contents of a zip file, check this article: See List of Files in Zip in Linux.