You already have speed() and bounce() functions called (in comments), but not declared. The basic principle of velocity is that you add it to the location. In this case, you add speedX and speedY to x and y, respectively. When you get more advanced, you'll get more values, such as acceleration, drift, etc.

Upon further inspection:

• First, why do you import traer physics if you never use it?
• Second, you shouldn't name variables beginning with capital letters (to avoid confusion).
• Third, you create twenty particles in setup() with the mouse location (which hasn't been defined yet!) and, thus, will be at (0, 0). I will explain a better way to do this...

The better way to do this:

Use an ArrayList, which is a dynamically resizable collection... in other words, exactly what you need. What you attempt is not impossible with an array, but it is made much more difficult and costly (to the frame rate).

Because you can always add and remove elements, create the ArrayList empty, then add a new element every time that the mouse is clicked. When enough time has passed, you can remove it.

Also, you'll need to loop through the ArrayList every frame - that is, in draw() - so that the elements can be updated every frame.