Not available yet: Text-to-bid is not turned on for events today. This article describes how it will work. Until it is on, guests bid on paper bid sheets. See Paper bid sheets.
Text-to-bid lets guests bid without downloading anything. Each item has a bid code. To bid, they text:
BID [code] [amount] — for example BID 14 350.
They get a confirmation text, and if someone outbids them, an automatic "you've been outbid" text. The instructions and number show on your auction page and can be printed on table cards.
Text-to-bid needs a Redswing text number to be set up first. That is not done yet.