Vi and Vim are ultimately the same thing. Vim is just the improved version of Vi. Vi/Vim is a text editor that is used in PuTTY when using comet.
Vim is needed when running molecular dynamics simulations because it allows you to quickly edit files and check results in output files. But, Vim isn’t your average text editor. Since it is designed for software like PuTTY, it makes editing very easy. The easy editing and the ability to edit your files in any way makes Vim very powerful.
Vim has many commands that contribute to how powerful the text editor is. Some of the helpful commands in Vim are :wq, i, u, G, gg, and :help cmd. Command, :wq, saves all the edits you have done to the file. Command, i, enables insert mode, which allows you to insert and delete things. Command, u, undoes previous action. Command, G, moves to the end of the file. Command, gg, moves to the beginning of the file. Command, :help cmd, gives you help about whatever cmd is. cmd can be anything you need help with.
One amazing thing about Vim that is helpful and essential is vimtutor. Vimtutor is a multi-lesson tutorial on how to use and gives you important commands to use Vim. Each lesson have many parts to it. If you go through the entire tutorial, you will be about to effectively use Vim. There is a learning curve though. It takes a while to get use to, but after practice with Vim and using Vim, you’ll be a pro.
Above is the beginning of vimtutor.