Why my sculpt brush is so blocky

I’m begineer for the blender2.79 and followting the tutorial on youtube , trying do some modeling by self but the most confusing me question is my brush whatever setting :detail size 10~40,Relative Detail,Subdivide Collapse. The model become so blocky not smoothly like the tutorial.
Whats the difference setting here ,how to solve the problem as I can not modify details at all.

A Relative Detail Size of 40 px creates bigger faces than a Relative Detail Size of 4 px.
A Constant Detail resolution of 4 is a low resolution producing bigger faces than an higher Constant Detail resolution.

So logic is inverted between both methods.
Relative Detail , lower number gives an higher definition.
Constant Detail, higher number gives an higher definition.

But maybe, you are referring to shading. By default, dyntopo mode is forcing flat shading.
You have to enable Smooth Shading option to perceive mesh as a whole without appearing faces boundaries.

Wow,Thanks Zeauro.Your explaination solve my headache long time as tutorial timeslapse not mention so clearly. Alwasy increase the detail size. Now smaller detail in relative detail is so smoothly.
Thank you!