There are a bunch of Screw types to choose from:

Screws for wood

Countersunk (Senkkopf)
Pan Head (Linsenkopf)
Try to use either Pozi (similar to Phillips) or – best – Torx heads

Screws for plastic

There are special Thread-Forming Screws to screw directly into plastic

Machine Screws

This probably the type of Screw most important to what this wiki is about.
Metric Thread machine screws can be used to connect almost everything to almost everything else.
Metal to metal, metal to wood, plastic to glass.

They come in different sizes named after the outer diameter of the thread. (e.g.: M1.2; M12)
Common sizes are:

• M2 or M2.5 for Electronics
• M3, M4, M5 for small to medium sized mechanical and mechatronical projects (I would mostly stick to those)
• M6, M8 and occasionally larger for load-bearing and bigger installations

There are – again – different types of heads to consider.

• Cylinderhead (DIN 912 or DIN 7984)
• Countersunk (DIN 7991)
• Pan Head

Machine Screws can be screwed into variously manufactured threads

Specialty screws

Grubscrews (Madenschrauben)
Shoulder Bolts
Studs