Groups in Power BI
This article describes how to create "groups" in Power BI Data Model.
Group is quite useful when you need to split values in some column to groups in other column. For example if there were workdays in some column (Monday, Tuesday, ... Sunday), we can make new column with "Workday" and "Weekend" values.
You can do it by IF in DAX (or another functions like OR...), but it is much easier with Groups.
How to create Groups?
You can create them in Data Model by going to "New Group" and them add values from left to the groups on the right side.
Or you can go to some visual, keep Ctrl, select few stripes (columns etc...) and then use the right click to Groups creation.
The result is totally the same - new Group appears in the Data Model as a new column.