Helpful Resources for Vim: #1 OpenVim

OpenVim

OpenVim Tutorial, according to me, might be the best hands-on approach to vim, though a bit restrictive. It has got great layout and pretty great introduction to the basic vim shortcuts.
There's an editor screen which shows the tutorial and where you type and use commands, then there's the keyboard that flashes the key you're supposed to press, and finally the sections to skip chapters or to practice again.
Tutorial can feel somewhat restrictive as other than the keys you're supposed to press, you can't use any other commands, not even keep on practicing the same thing till you get it. You either start the chapter anew or switch to the practice mode.

Also there's this practice mode on the website where you get an editor screen and a helpful sidebar of context-aware actions to see the list of rightful changes.

Viewing long output and scrolling up/down in tty terminals

To view long output from utilities like ls, 
you need to pipe the output into a pager, such as  
more or less : `ls | less`

The `|` (pipe) sends(, or pipes), the output from the command on the left (ls) into the input of the command on the right (less) as arguments. 

• Press the spacebar or `f`  to scroll down the output by a page. Or `d` for half-a-page.
• Press `b` or `ESC-v` to scroll up the output by a page. Or `u` for half-a-page
• Press the `q` key to quit the pager. 
• To search for some text type `/something`
• Try `man less` for more information.

 To scroll up/down in a terminal without support for mouse, just press `SHIFT + pgUP/pgDOWN`. Although the amount you can scroll depends on terminal's scrollback buffer.

Now, to increase scrollback buffer size-

• Press Ctrl-a then : and then type scrollback 10000
• to get a 10000 line buffer, for example.
• You can also set the default number of scrollback lines by adding defscrollback 10000
• to your ~/.screenrc file.
• Another tip: Ctrl-a i shows your current buffer setting.

Relative line numbers in Vim for calculation free fast movement

I've seen on someone's Vim having dynamic line numbers. You can just switch to another line by looking at its line number and using that with either j or k.

So, after googling a bit, I came upon these settings-

" To show normal line numbers
set number

" To show relative line numbers
set relativenumber

Just add one of the above snippet to your .vimrc and you're good to go.

But,  if you want to toggle between them, 

See this post by Jeff Kreeftmeijer

Jeff Kreeftmeijer - Relative line numbers in Vim for super-fast movement