those are tools to add to your toolbar. if they're grayed out, it's because they are already in your toolbar.
your fluid brush has note. arrow over it over click it to see the issue:
Those tools are not in my tool bar. They just grayed out. For example, where is the oval tool in my tool bar ? Can you see ? I can't find. Moreover, I clicked the note but it doesn't open. There is not a note which I can read. It is just warning sign.
Ok. I kept it pressed and others are appeared. But fluid brush still doesn't selected.