the noun form of turn is used to refer to a specific instance of something turning or occurring. It's often used to refer to a change in the course of events or direction, or the motion of something that causes it to rotate around a central axis. It can also refer to something more specific, such as a single rotation, a shift or transition.
1. The turn of the screw changed the outcome of the experiment.
2. That was a sharp turn around the corner.
when talking about a wide range of turns, be sure to specify the 'amount' of turns in the phrase (e.g., a full turn, a half turn, etc.) Remember that when 'turn' is used as a noun, there is no need for a prepositional phrase.
the verb form of turn has a variety of uses. It can act as an intransitive verb, meaning it needs no direct object to complete its meaning ‘He turned around.' It can act as a transitive verb, indicating a direct object is needed to complete its meaning 'He turned the key.' It's also used as part of phrasal verbs (e.g., turn away, turn over). When used as a verb, it has a variety of meanings, such as to move in a circular direction, to change direction, to cause to move around an axis or center, to start or stop something, to cause to move something, or to change something.
1. He turned the page without finishing the chapter.
2. The wind turned the tree branches in circles.
3. I'll turn the TV off for the night.
when using turn as a transitive verb, be sure to include the direct object immediately after. As many uses of turn are related to motion, it is important to specify the direction of motion implied. Comma placement when using turn can be tricky. If you're using it as a standalone verb, no comma is necessary. If you’re using it as part of a phrasal verb, a comma should be placed between the verb and the prepositional phrase.