This collection of files exists to serve you as starting point in exploring different sounds and how they're programmed in Sonic Pi.
Copy & Paste them into your Sonic Pi editor and start tweaking the values to change the sound.
The Sonic Pi integrated editor has a lot of keyboard shortcuts. A handy list of all shortcuts is integrated in the tutorial browser or online on github.
This image explains nicely, the four important parameters to controlling played sounds in Sonic Pi.