Enter the anchor relative (G0), then add their children (G1), then those children's children (G2), then theirs (G3 — usually you, the applicant). Optionally add G4 (the applicant's children). Your entries are saved as you go.
Use Export JSON to download a copy of all your data. Keep that file somewhere safe — cloud storage, an external drive, an emailed copy. Import JSON replaces everything currently here with the contents of a file you exported earlier. Reset everything erases all relatives and documents and starts fresh; there is no undo.