Vim: How to insert in visual block mode?

Try this

After selecting a block of text, press Shift+i or capital I.

Lowercase i will not work.

Then type the things you want and finally to apply it to all lines, press Esc twice.

If this doesn't work...

Check if you have +visualextra enabled in your version of Vim.

You can do this by typing in :ver and scrolling through the list of features. (You might want to copy and paste it into a buffer and do incremental search because the format is odd.)

Enabling it is outside the scope of this question but I'm sure you can find it somewhere.

1. press ctrl and v // start select
2. press shift and i // then type in any text
3. press esc esc // press esc twice