Custom effects in WLED MM

I just can’t find a tutorial that explains how to create customer effects that I can select later and the interface.
I have often done this with FastLED in Arduino.
Here are two examples of what I want to do:

  • Simple running light, using spacing and grouping in the segments. Selection of the speed and the two colors. Background light and light of the running pixels.

  • All LEDs are to be divided into three random groups that are switched on and off in quick succession. Selection of colors, selection of speed.

What is the best way to do this? I see usermods more as a way of integrating additional components such as I2C devices, etc.

I would really appreciate a link to instructions for my problem or other tips.