How to create SAPUI5(Fiori) library in Web Ide?

Dear experts,

Could you please advise how to create properly a custom library in Web IDE?

What I found is a description like this:

SAPUI5 SDK - Demo Kit

However here is completely unclear how to create properly a project.

Should I create only manifest.json or .library or both of them?

Also I noticed: there is a special project type Fiori library in Web IDE but it's not active and it's not possible to choose it.