Hi,
Well, this is one of those questions that look simple but turn out quite complicated 
Without going too much into the details, the controls let you pick any hue and a wide range of saturation/chromaticity (let’s consider them the same here) values. In order to select an arbitrary colour, you still need a 3rd dimension, that is the lightness/brightness. Plus there is the issue about what is the working space, what is your output space, what your monitor can display, and ultimately what is colour itself… but let’s not get there as it’s a big can of worms (and not something I really understand…, So next question)
Perceptual uses a perceptual color space for separating hue, “saturation” and “lightness” (i.e. Jzazbz), whereas normal uses a linear RGB space. As a rule of thumb, use perceptual.
The picker will select a combination of hue/sat that will neutralise the colour you pick. You can use it to remove colour casts or for some kind of local white balancing (it’s not quite the same as a “proper” wb, but for not-too-extreme corrections it works fine).
HTH