What are the different ways to enter Insert mode in VIM?

Question

Accepted Answer

i/a insert before/after the cursor, I/A jump to line start/end, o/O open a new line below/above — all then start typing.
The point is that you pick the entry key that already puts the cursor where you want to type, saving a navigation step. Lowercase acts at the cursor, uppercase acts at the line edges, and o/O make fresh lines.
Multiple ways to enter Insert mode from Normal mode:

Key
Insert position

i
Insert before cursor

a
Append after cursor

I
Insert at beginning of line

A
Append at end of line

o
Open new line below

O
Open new line above

Visual guide:
    Hello World
      ^
      cursor here

i = insert here: |Hello World
a = insert here: H|ello World
I = insert here: |Hello World (line start)
A = insert here: Hello World| (line end)

Tip: Use a when you want to add text right after the current character, i to insert before.

Key	Insert position
`i`	Insert before cursor
`a`	Append after cursor
`I`	Insert at beginning of line
`A`	Append at end of line
`o`	Open new line below
`O`	Open new line above