Maximum bid is the highest amount you are willing to bid and auction for, and autobid automatically increases your bidding amount when other bidder bids an amount higher than yours. Autobid will stop when the bid amount exceeds your maximum bid amount or when you win the auction.
 Example:

Current Bid: RM 7.00

Your maximum bid: RM 200.00

A bidder joined in the auction and placed his bid at RM 8.00, now autobid will help you placed your bid at RM 9.00. Autobid will continue and will stop when there is bidder place RM 201.00 as his bid (autobid was stop due to your maximum bid is RM 200.00).