Each signed-in user can give up to 10 yellow stars per Flipnote. Yellow stars do not use your colored-star balance. Green, red, blue and purple stars are spent from the balance stored on your account.
You can favorite Flipnotes and post normal text comments when comments are enabled. Memo comments are a Flipnote Studio feature: existing memo-comment PPMs can be viewed or downloaded, but the website and personal API do not accept arbitrary memo-comment PPM uploads.
You cannot star your own Flipnote. RexiMemo also checks colored-star balance before accepting a colored-star action.