Log stats after each game and the leaderboards, team totals, and player pages update themselves. Everything is saved on this device only. Back up often with Export on the Data tab — that file is your season.
Type numbers, then hit Save. Blank = 0. Only players with a stat are counted as playing.
Your stats live in this browser only. Export a backup after every game and keep it somewhere safe (Drive, email to yourself). To move to another device, export here and import there.