Do /auc start for more information. For example do /auc start 1 100 100 The 1 stands for how many you want to auction. The first 100 is How much you want to put the Bidding Start at. The next 100 is the Min Bid Increment.
You may sell things to other players but beware they might try to scam you. Scamming is allowed on the server.
To auc the command is /auc start Or /auc start (amount) (starting price) Be careful if you trade with people as scamming is allowed and people in prison do scam. And you can only auction: Creeper eggs Diamond Armor Diamond Tools Beacons