The option for "Single Bid" or "New Group" is defined as follows:
Single bid is the default setting, you simply place a bid on that lot. New group is used to set up either/or bids. For example, if there are multiple lots that you are interested in but only want a select number from that group you would select new group. The first lot you bid on would be marked as Group "A" and the next lot you bid on you will be able to select group "A" to group them together, there is no limit to the number of lots you can add to an either/or group. Once you have done this you can also select the number of lots within that group you would like to win. You can create as many groups as you like.