There are three common types of touchscreens:

1 – Capacitive

Invented in 1965, started catching on by mid 1980’s
A capacitive touch screen consists of a glass panel with a capacitive (charge storing) material coating its surface. Circuits located at corners of the screen measure the capacitance of a person touching the overlay. Frequency changes are measured to determine the X and Y coordinates of the touch event.
Require electricity to flow through whatever is touching it… based on moisture content
This is why your finger and a rubber tip will work but a hard plastic stylus will not
Inexpensive and rarely have batteries or buttons
Capacitive type touch screens are very durable and have a high clarity. They are used in a wide range of applications from restaurant and Point-Of-Sale use to industrial controls and information kiosks.
Problems: few with “palm detection”, not pressure sensitive
The few with buttons and batteries use Bluetooth to talk to the device

2 – Resistive

An overlay on the screen with a transparent spacer in between.
When pressure applied the two layers touch and an electric circuit is created and it know where you are
Cheap, not very nice feeling – a bit squishy and definitely not precise – I see in cars

Latest technology – have a grid over the screen for location and use Bluetooth to talk to the device for buttons
Transparent grid overlaid on the screen
When you get NEAR the screen with an active stylus the mouse will move to that location
Most accurate but still problems with diagonal lines because the grid is square
Has palm rejections and pressure sensitivity
Expensive $50-$200+
Can be made to be specific to the device, the Apple Pen is locked to ONLY work on devices Apple wants it to

In this video we discuss Dell 557W, Dell 556W, Dell 579X, MS Surface Stylus, a rubber tip, finger and a generic active stylus on a Microsoft SurfaceBook, Dell Latitude 5300 and Dell Latitude 5490.