Pioneer Dj DDJ-FLX10 4-Channel DJ Controller for rekordbox and Serato DJ Pro (Black) - Manual (Page 13)

Part names and functions
13
En
Press:
If the cursor is pointed to a track, the track loads onto the deck.
If the cursor is pointed to a library or
[crates] , the cursor moves between the
library and [crates] panels each time you press the button.
Press twice:
Loads the track from the deck that isn't playing onto the deck that is playing.
If you do this while the track is playing, it plays from the same position (Instant
Doubles).
2 BACK button
Press:
Moves the cursor between the library and
[crates] panel each time you press
the button.
Hold:
Launches Utilities mode.

Read more: Changing the settings (page 154)
[SHIFT] + press:
Loads a track onto the [PREPARE] panel.
3 VIEW button
Press:
Changes the screen layout of Serato DJ Pro.
[SHIFT] + press:
Changes the panel display each time you press the button.