Trading on Analog.Games works similar to a stock exchange.
The seller specifies his desired price (the ask) and interested parties can bid on it by submitting a bid.
This goes back and forth until the last bid coincides with the last ask, then the trade is concluded.
You can change the bid and ask as often as you like, so that the seller can also adjust his asking price.
If you want to buy a game immediately, use the 'Buy Now' button, which does all the work for you, that the trade is instantly concluded.