This is a new mode (at least for me). So for instance, if you want to add say a # in front of a bunch of lines, you can do a redo over and over, but the visual mode is a nice way to think about it, you just hit ctrl-v and then your selection keys like j or k select a block of text.

The trick is that when you want to insert something you type Shift-I that is a capital I and it inserts. I really wanted just to do a lower case I and then you end the insert mode with an ESC or a Ctrl-C.

Of if you want to change a block, then it is Ctrl-V and then select the block, then c moves you to change mode and everything you type will change what ever was in the block.