Want it to keep going? Snap on the block if on edge, bounce.

Then, click the Control category. Wrap a forever block around the other blocks, like this:

Click anywhere on the stack of blocks to try it.

To stop, click the stop button:

Want it to go at an angle? Snap a point in direction block on top, and type in an angle.

Next, click the Events category.

Drag out a when clicked block and snap it on top:

Your script will start whenever you click the green flag: