Vim (and vi before it) has a command set that is a composable language.

First, you have motions. These are actually the nouns of the command language, but on their own they mean cursor movements. There are a whole lot of them. h is left, l is right, j is down, k is up (all one character). $ is end of line, ^ is beginning of line, ( and ) are beginning and end of paragraph. That’s enough for now (but there are heaps more).

Then you have verbs. Verbs are followed by a motion to make a sentence. d is delete. dl is delete next character, dh is delete previous. So now you can guess that (d) is delete this paragraph, d$ is delete the rest of this line… and so on.

Double a verb to apply it to the whole current line… dd for example.

Prefix it with a number to do it that many times… 55dd deletes the next 55 lines.

So how do you actually put stuff in to a file?

• i lets you insert stuff in front of the cursor (it’s an exception because it doesn’t take a motion). After you type i you’re in insert mode; press the ESCAPE key or control-[ to get out. Note that vim starts in view mode, you have to type a command to get in to insert mode to start typing stuff.
• s means substitute, and it will replace the motion with whatever you type. sw is substitute word, and a command I use a lot. ss is substitute current line.
• a means append, and it’s exactly like insert except it goes the other side of the cursor.

There’s a bunch of verbs for useful things like cut and paste.

• Delete is actually cut
• p pastes after the cursor
• P pastes before.

Lastly, : lets you into vim’s other main mode, command mode, which has a lot of power. Something like:

• :w is the save command
• :q is quit.
• You can combine them as :wq.
• Help is :h.

So, that command set as language idea makes vim completely different from other editors in how it sits in your mind.

Original content source: Andrew McGregor, Performance Measurement Lead at Fastly (2019-present), who've answered it here.