A few of the following settings can control the general length, thickness, etc of hair. All of this does tend to assume that the mesh object is at a default scale/rotation, which is vital for any type of particle/dynamic/physics type system. In order to do that, select the object and press Ctrl-A and select Rotation & Scale.
With that done, Under Emission, Hair length will control the general overall length of the hair. Depending on how long your hair is, you may want to increase the initial number of Segments in the first lot of settings.
Usually you only have a smaller number of main hairs under Emission and then use Children hairs to fill out the rest, that’s also where you can setting Clumping, which will ‘pull’ the ends of hairs together, a bit like those sample images.
For overall thickness, this is controlled under the Cycles Hair Settings, but keep in mind, that will only really show when you render the image, it won’t adjust how things look in the basic viewport.
Another thing to keep in mind is that you can have more then one particle hair system on any given mesh, just by using vertex groups to control where the hair from each system appears.
At this stage, I’d more suggest having a search on Youtube for some basic hair tutorials for Blender, since at the end of the day, things can get very complex, very quickly and then animating it is an even bigger nightmare.
After which it’s just a matter of spending time and playing around with it all so you can slowly understand how it all works.