Basic Vim concepts

vim index.html    open a file

i - go to insert mode:
  
: (just colon)   access command palette:
:help help
:w write file:
:q quit file:

x - to delete the unwanted character
u - to undo the last the command and U to undo the whole line
CTRL-R to redo
A - to append text at the end
:wq - to save and exit
:q! - to trash all changes
dw - move the cursor to the beginning of the word to delete that word
2w - to move the cursor two words forward.
3e - to move the cursor to the end of the third word forward.
0 (zero) to move to the start of the line.
d2w - which deletes 2 words .. number can be changed for deleting the number of consecutive words like d3w
dd to delete the line and 2dd to delete to line .number can be changed for deleting the number of consecutive words

in case vim was not closed correctly, there is a .swp file and vim is complaining when you open it again.
then just delete the swap file:
  rm .file.swp
  rm .file.swo
  and so on