Without going into excruciating detail, the preferred G shares would pay a dividend, I believe at a fixed rate if I recall.
The S-1 was to authorize a public offering of the G shares, and the S-4 was to authorize an exchange of existing common shares for the new G shares, at a somewhat better rate than the public offering.
I think the SIAF investor page has a more complete description, in the press release that announced them, which was filed in early 2019.