See also Prone (Condition Type)
Prone - Can't move or take
Actions, 
Bonus actions, or 
Reactions, and has 
Disadvantage on 
Strength and Dexterity saving throws. - Attacks against a Prone creature have
Advantage if they're made within 
3 m / 10 ft of the creature. - A Prone creature must spend half its Movement Speed to stand up.
- A character with the Athlete feat spends only
1.5 m / 5 ftof Movement Speed to stand up.
- A character with the Athlete feat spends only
Sources of Prone
Notes
- Proning an enemy does not mean they skip their next turn, they will simply use their movement to get back up.
- however if you get proned during your turn, you automatically end it.
- Proning an enemy and reducing their movement speed to 0 will skip their next turn.