How to fill up "Title" "Drawn by" "Revision" etc...?

I'm not sure what problems do you have with it.

Just add text objects with contents you want in your schematic.
Or make a new title page containing all that info and place it
into your project's symbol directory, then define default
titleblock in your project's gschemrc, use something like
  (define default-titleblock "my-new-title.sym")
and all new project pages will use it when created.

There is no specific way to fill in this information, you could just use regular text objects.

If you prefer a more semantic approach, you can select the titleblock (if it's locked, you can select it via "T L" in the latest development version of gschem), add attributes "Title=My title" etc. (via "E E"), and set them to show-value and the desired size (via "T V" and "E X").

It may be convenient to create a custom titleblock which already contains these attributes, like Vladimir said. I personally prefer using a titleblock with pre-defined attributes and without a page boundary, so I can simply draw a box to fit the page contents.

Here's an example of how such a titleblock may look like:
http://www.gedasymbols.org/user/kaimartin_knaak/essential/symbols/titleblock/titleblock.sym