that is very simple.

you have three balls, they bounce at the screen borders.

they are connected by lines

see for bouncing
http://processing.org/learning/topics/bounce.html

see for line
http://processing.org/reference/

To make the lines disappear you can use something like this:

Sure, no problem.

On another note: Please read the forum guidelines - Annex C

Your current topic title is generic, non-descriptive and incorrect (since you don't provide any code).

So in the future make sure to use more descriptive topic titles. Thanks.

Restored.

Do not remove threads that have answers.

This is rude against the people who have answered your questions and it is against the philosophy of the forum, which is of course about sharing knowledge. Other may benefit from the information and examples on the forum as well. Trying to cover up when others have (apparantly) helped you with homework is futile, because all moderators can restore threads.