Not "Jhunka", Junk + a, like trash.
I use this brush to draw other brushes. I tend to be a little "sketchy" with my lines with it, where I do a bunch of search lines, and so I call it my junk brush for encouraging bad habits.
Let's talk a little on brush philosophy for a second. Despite making both free & paid assets for clip studio paint, I really do think you can have all the tools you need with just a few brushes. Once you find a drawing brush, a lining brush, and a coloring brush, that are all comfortable to your hand, you're perfectly fine. Everything else is just extra. The artist makes the drawing, not the tool. The tool is only there to make things easier. That's what this brush is.

Top is "Junka Brush" with Color Mixing: OFF. Bottom has Color Mixing ON. Both give a different line feel for line art & coloring, and both can be used for anything. It's a basic brush with a round tip I use from start to finish on basic illustration projects, like so:



Rough Sketch -> Cleaned Sketch -> Initial Line art -> Cleaned up & Thickened Line art -> Flat Colors -> Shading & line coloring. All this was done with the Junka Brush. Adjust the speed and such to your liking.
This brush is nice for illustrations where you build up little details, as it tapers/loses density for smaller lines, giving the illusion of them being even thinner.
I included a basic variation here, the Frosted Junka Brush:

I like it with color mixing on the best. It looks like frosted glass.
Here's a comparison below with a basic doodle between the two brushes:

The basic brush on the left, the frosted on the right.
It can look like a pencil/thin pen when small, like so:

Some very fluffy 80s hair to demonstrate the contrast. I think coloring looks the best, but it is up to you. I also used the regular brush to draw all these stamps:

Anyway, do whatever you like with it. Adjust it to your needs & have fun. Remember: make every tool comfortable to you. :)
artistic junk food