Pop-up windows, in this context, are browser windows that either appear on top of the page you are looking at or open in a new browser tab. For instance these help pages are pop-up windows – they open in a new window or tab when you select them from the DutyMan menu.
Pop-up windows are very useful because they can be opened from a page and that original page stays open rather than being replaced. For instance you might be looking at a DutyMan page and need some help on how to use it. Clicking a help icon opens a help page yet leaves your original page intact.
It’s also easy to pass information to pop-up windows, for instance start and end dates when printing duty lists.
Unfortunately pop-up windows are also very useful to advertisers. Apparently adverts are more successful when annoyingly popped-up. Hence the need for Pop-up Blockers. Pop-up Blockers suppress the “bad” advertising pop-ups but, unless they are particularly clever (and many now are), they also block “good” pop-ups. This can make it appear that parts of applications such as DutyMan are not working.
What to do
If you find that parts of DutyMan don’t seem to be working, typically you click something and nothing happens, then it may well be due to pop-up blocking so try telling your Pop-up Blocker (it’s normally, but not always, part of your web browser) to allow all pop-ups from dutyman.biz.
If it’s not obvious how to do that try searching the web for something like “firefox allow pop ups for a site”.