vi is a free software screen-oriented text editor written by Bill Joy in 1976 for an early BSD release.Vim, which stands for Vi IMproved, is an open source, multiplatform text editor extended from vi. It was first released by Bram Moolenaar in 1991. Since then, numerous features have been added to Vim, many of which are helpful in editing program source code. Vim and vi are very popular editors for programmers and users of Unix-like operating systems.
No doubts that learning vi or vim is not easy for Linux newbies. This sheet (from viemu.com) describes the full vi/vim input model, the function of all keys, and all major features. I use it as a compressed vi/vim manual.
Hope it helps!