Change all characters in a column over multiple lines

Use vim in column mode. To use it, press:

1. Ctrl+V to go into column mode.
2. Select the columns and rows where you want to enter your text.
3. Shift+I to go into insert mode in column mode.

4. Type in the text you want to enter.

   ^{Note: Don't be discouraged by the fact that only the first row is changed.}

5. Esc to apply your change (or alternately Ctrl+C).

You will now see your changed applied.

Source: Column Edit Mode in VI.

Use Ctrl+V to enter blockwise visual mode. You can then select a block of text using the normal movement keys and press x to delete it. I will perform a multi-line insert.

See :help ^V and :help visual-operators in vim for full details.

Use Ctrl-V to select in block mode, then directional and editing commands to do the rest. See How to remove quotes surrounding the first two columns in Vim?

You're looking for Visual Block mode, which is accessible by Ctrl+V in Normal mode. Works just like Alt+select in TextMate.