Dropdown in one column fills another column

First things first: I'm a hardware tech but know doo diddly squat about programming or function building in a spreadsheet.

I have created a dropdown list in column D. I'd like each selection to auto-populate a value into column B of the same row.

I'm presuming I need to use VLOOKUP for this, but am stuck on how to do so. Feel free to explain it to me like I'm 5