Piano Online 123
If you're searching for "Piano Online 123" you're probably looking for a numbered piano keyboard that you can play online.
It's a good place to start. Online, virtual pianos work in many different ways, but the main distinction is whether you play it on a touch screen with your finger (tablet, phone) or a desktop (with a mouse.)
An online piano allows you to try playing piano without actually buying a physical instrument. You can always buy an inexpensive keyboard for $100 if you are still interested.
The distinction between a virtual (online) keyboard and a small, inexpensive electronic keyboard is one of dimensions. Online is really only two dimensions, whereas an actual keyboard, however simple, has numerous dimensions (white keys, black keys, etc.) that you must explore.
Even on a two-dimensional, online-virtual piano, you will see the pattern of the black keys: 2 blacks, then 3 blacks, repeated over and over. This black key pattern (2-3-2-3-2-3) is one of the indelible signposts that will help guide you as you begin to explore the keyboard.