Good resourses to learn PCB designing
The key to learning anything is knowing the best keywords in an iterative process. 

In your case ; PCB DFM  IPC Standards

Then for visual learners or ESL learners use images.

If you do not learn the Design Rules for Manufacturing and IPC standards for layout, thermal pads, gap, materials, stackup designs etc, looking at online sites may be bad examples with poor practices by those who want help.   I would not recommend any one site shared by newbies.