Although it sounds like this should be simple, it isn’t. You need to remember if the LED is on or off (probably a flip-flop), the brightness of the LED (probably a buffer), and the current mode (on/off, brighten, dim; maybe a couple flip-flops).
There are also additional questions that need answered. What happens if second button press is short? If it just turns off the light, there is no reason for a 3 second press to turn off light after bright adjust; third press will do that (or long press can put it back into bright adjust mode). If you are not doing that, what would a third button press do if it is short?
I’m not at my computer, but I’m guessing you can probably use debounce node to determine when it is a long button press.
One option for controlling program mode (on/off, brighten, dim) is to use gate nodes to disable button press for parts of program for modes that are not currently active.
If you want light to slowly get brighter/dimmer while holding button, you will need some sort of delay between each time you add or subtract from current value.
Lots of information to get you started. If you are trying to learn and not just have the answer given to you, it will generally be better for us to help you figure out what you are doing wrong rather than us giving you a working program.
If you don’t know what you are doing, it is best to start with a small part and get that working, then add another part. In this example, get LED on/off working, then add a tweak node to set brightness while it is on, then figure out how to replace the tweak node with a buffer and use the button to adjust brightness (you may even want to make a separate program just to adjust a number with button, then figure out how to merge it into LED on/off program). You want as few unknowns as possible when trying to combine everything together, or it will be difficult to narrow down where any problems are if it doesn’t work. As you begin to understand XOD and programming better, there is more you understand before you get started and you can work in bigger chunks.