The MIDI Track Picker adds a MIDI track from a different style to the current song.
For example, add a Strings track from a Bossa style to the Strings track of your current song. Open the dialog and
choose a Band-in-a-Box track. Then choose the style and the source track that you want to add.
To see a full description with screenshots, step by step, open the Help inside BB by selecting the Help menu -> Topic Search.
Then enter "Strings" into the LH search pane and hit the List Topics button.
Scroll down that list and find, MIDI Track Picker.
Doubleclick on MIDI Track Picker to view the good stuff on RH side large window.
Adding the Strings from any Style as a separate track is easy to do. Worth revisiting and auditioning strings from a few different styles that may seem to match your project's tempo and fell until you get "just the right one".
The above saves you from having to "roll your own" strings parts and takes advantage of the fact that the Strings parts in the already existing styles were developed by the experts on the pgmusic staff.
--Mac