Ten minutes, nothing to write.
1Get a visual
One is already playing. For more, the library: download a zip, unzip it, keep the folder somewhere you will find again. Your own GLSL or p5 sketch works the same way; what Sialk plays says the shape a folder needs.
2Add it
Drag the folder onto the Sialk window, or press ⌘O and pick it. It starts at once, at the top of the stack.
3Mix it
Click a layer's card to select it. Opacity is the amber bar: drag it. Blend is the dropdown: normal, add, screen, multiply. ON at the top right switches it off and on. Two layers and one blend mode is already a show; try add with the top layer at about half.
4Give it music
Play something and make sure Sialk can hear it; the fastest way is the built-in microphone with your speakers up. Every library visual listens to the room, so it starts moving now. Better routes: play music into it.
5Play its controls
The selected visual's controls are on the right: colour, speed, how hard it reacts. Drag them.
6Put it on the wall
With a second display connected, the picture is already there. Press f for fullscreen on one screen; Esc brings it back.
7Keep it
⌘S saves a .sialk file. Reopening puts everything back as you left it.