how to do skin just like reality?

That image is an example of particle projection not bump or displacement.  Bump and displacement are greyscale height maps.  Depending on the program/render engine used black represents 0% or -100% bump/displacement and white represents 100% bump/displacement.  Bump is a shader illusion that doesn't change the mesh it just gives impression of added dimension.  Displacement actually changes mesh by displacing new 'micro faces' along the normals of the actual faces.

thanks boy

Is that like a Flavor Flav "Boy"? Or are you infering that jestmart is an adolescent male? Generally the word "boy" is a little patronising where I come from?

Maybe you'd get more responses to your questions atpo if you defined them a little more clearly rather then just broad generalistions. For example your question above are you asking how to make bump maps or apply them or how they work? 

i am sorry for the word "boy",thank for your suggestion,MR razor.

here i use the word "webfriend",is it ok?is it misunderstand again?

Lol, webfriend is fine by me. i'm getting vague tingling that english may not be your first lanquage?

Its all good, sometimes things can just come across in ways unintended in writing. I'm sure you didn't mean any offense.

When your asking a question try to be specific as possible it'll give more chance of someone responding with the information your looking for.  

Here I am from shanghai China.Nice to talking to you.

I have read your product ,nature scene ,dragon,is your favor,and the space,time stone-zone