I don't want all the sections to be visible all the time. The user should see only a few fields first and the rest of the fields should appear as the person keeps filling. What is the process?

It's quite easy to do this, it can be implemented on both sections and modules. you just have to mention the condition in "display this if" and you are done.

eg- 

You can also use = if the reference module is a single selector, you can also show a module or section to a particular person by limiting the display if field to the personal email or name, etc. 

You can do that by simply adding a visibility condition at the section level. From the second section onwards, you can add a condition to show the section if the last field on the first section that is not blank. This can be repeated simultaneously for the other sections as well.