A custom report allows you to take an existing report, set the filtering to whatever you want, then save that so that it appears in your Custom Report List. Your Custom Report list shows in the Stats section, and there's a Custom Report Widget that you can add to your home page. This allows your players to click on that report and all the filters will appear as you have pre-selected them.
As league administrator, your list of saved Custom Reports will show in the Administration -> League Info section. You can edit the details of the report, view the report, or change the order that the report is displayed
You can edit your home page layout and add the Custom Report Widget for your players to have quick access to them, or they can go to the STATS section and your custom reports will be listed there under a new Custom Reports heading.
The main League Standings report is unique in that does not have the option of a Custom Report. However, it has several settings which you can configure in your League Settings. Go to Administration -> League Setup -> League Settings -> Change League Settings, and choose the "Standings" option from the Category drop down, and you'll see numerous settings which affect the default display of your League Standings report.