Soccer Rules Corner Kick

Referees are reminded that opponents must remain at least 9.15 m
(10 yds) from the corner arc until the ball is in play (the optional marks
off the field of play may be used for assistance). Where necessary, the
referee must warn any player within this distance before the corner
kick is taken and caution the player if he subsequently fails to retreat
to the correct distance.

See the training video info HERE for more soccer skills.

If the kicker touches the ball a second time before it has touched
another player, an indirect free kick is awarded to the opposing
team in the position where the second touch occurred (see Law 13 –
Position of Free Kick).

If a player, while correctly taking a corner kick, intentionally kicks the
ball at an opponent in order to play the ball again but neither in a
careless nor a reckless manner nor using excessive force, the referee
must allow play to continue.

The ball must be placed inside the corner arc and is in play when it is
kicked, therefore the ball does not need to leave the corner arc to be
in play.