The button (Icon) Insert line-group, you will find in the Tool bar Tab (Category <Page>.
Hereby you insert a main-line for a new voice-group.
Main-lines you can recognize in the score if you pay attention on following property of Main line(s):
They have angular bracket between main-lines and it is not pulled through other main lines with strands per default.
If you want to insert only one sub-line of a voice-group, click on this button: .
Please do not confuse the functions: "Insert line" with "insert bars"!
If you want to insert only further bars in a voice in order to get a new line),
pick the function Insert bar(s) in the Tool bar Tab (Category) <Meter>.
The same function Insert bar(s) you will find in the Tool bar Tab (Category) <Form>.