Back in 2016, Double-Touches were and still are a meta defining mechanic. Being able to hit the ball into an hard to defend position and making a shot on goal will make the defending team panic and make mistakes. Advanced versions of this mechanic use the side walls, corners, and edges of the field to make it harder for defenders.
When the ball is in the air, Fast-Aerial and hit the ball towards the backboard. Try to hit the ball a little under the center to keep it in the air.
After hitting the ball stop boosting to give the ball some space.
Read the bounce off of the wall or corner and try to score.
A common way to start a Double-Touch is off of the wall. Rolling the ball up the wall and hitting it so that it hits the opponents backboard is a great setup for a Double-Touch. This way you do not need to wait for a high pass from a teammate. Setting up Double-Touches from the ground is possible but uses a lot of boost and is difficult.