Hi!
The digitizer is basically just the touch part of the screen and is mainly the upper glass layer of your phone’s display assembly. Usually phone touchscreens are composed of 2 components: a digitizer and a display.The digitizer is glued to the screen most of the times, but you can also get it as a separate replacement part. The problem is, digitizers are hard to separate from their screens, but some repair shops have the tools needed to separate the 2 parts, that’s why they can be found online.