i → Insert mode. Type ESC to return to Normal mode.
x → Delete the char under the cursor
:wq → Save and Quit (:w save, :q quit)
dd → Delete (and copy) the current line
p → Paste
hjkl (highly recommended but not mandatory) → basic cursor move (←↓↑→).
Hint: j looks like a down arrow.
:help <command> → Show help about <command>. You can use :help without a <command> to get general help.
a → insert after the cursor
o → insert a new line after the current one
O → insert a new line before the current one
cw → replace from the cursor to the end of the word