Selections are used to divide your log in groups of QSOs. Such a division can be based on a date range, on one or more group numbers, or some special flags like QRP and YL QSOs. 

Every QSO has a group number, that you can set manually, during a log import, or after the fact, based on some search criterion. A single Selection can use one or more of these group numbers.

After making a selection, all statistics, reports, needed lists, summaries, colors of packet spots etc. will only use the QSOs that fall into the specified selection. This way you can combine multiple logs into one big log, or just do an analysis of a contest you were in. 

Group numbers can have a text attached. So group number five could get the text 'CQWWSSB-1999' for example. Using group numbers is also more efficient than storing the same text in every QSO, and the text for a group number can be printed on a QSL label.

Above an example of a selection called 'QSOs in 1995'. Here we only use a date range and ignore the group numbers.