Flat heads are countersunk (cone shaped under the head) with a flat top. Slotted drive has a simple slot for a flat bladed screw driver.
Round heads are domed and look like half of a sphere. Slotted drive has a simple slot for a flat bladed screw driver.
Driver bits are available in various drive types and bit styles.
Screws with machine threads for use with a nut or in a tapped hole.
Screws with an Allen wrench drive.