Click the piano keys to play them. Click "Select tonic and scale". Then click a piano key to select a tonic, and click a scale name to select that scale. The "Change mode" buttons let you change the mode (shift the semitone intervals). Use the sliders at the bottom to change the sample melody and the tempo.
What is "scale", "tonic" and "mode"? The following website explains this and more in a clear and easy-to-understand manner: https://www.howmusicworks.org/ The scales I have used are from that website. It is by no means an exhaustive list of scales. If you want to use other scales, click the "Custom" button and enter the semitone intervals (e.g. 2212221 for the Major scale). Piano photo by Dolo Iglesias on Unsplash: https://unsplash.com/@dolodol
