EDIT: @vw_dorico
Anyway, here a short tutorial on how to insert that bar (but please, work through the suggested tutorials, too! ) :
Just remember that once you create the new voice with Shift+V and write at least a note with that new voice, you have now two voices living into your staff. To decide into which voice you want to write the next note, after activating the caret, you can switch the active voice pressing only V (without Shift!): you will see the little note change as described, according to the current active voice.
The shortcut V can be also use to change a selected note to the next available voice.