Hold one of the Search buttons (either forward or backward will work), and then turn the jog wheel. The needle will scrub at high speed in the direction the jog wheel is turned.
Press the hot cue button while touching the surface of the jog wheel. The track will jump to the hot cue location, but will not play until you let go of the jog wheel.
Using the method above, jump to the hot cue while touching the jog wheel surface. Then, before letting go of the jog wheel, hit the main cue button to set the cue location. When you let go of the jog wheel, the track will remain cued and will not play. This then makes it easy to, for example, set an instant loop from the cued location.
Press the backwards Track Search button. If not already at the beginning of the track, this button will reset the main cue to the first cue point of the track, and will pause playback. If pressed when already cued at the beginning of the track, the button will skip back to the previous track in the current playlist.
This will need Rekordbox for first-time audio routing configuration, but once set up, the mixer can simply be used with Audacity or any other DAW as an input source.
Firstly, download the relevant driver from the Pioneer website. For the DJM-450, the page is here: https://www.pioneerdj.com/en/support/software/djm-450/ If installing this on Windows, restart your machine after the install is complete.
To set up the audio routing properly, connect the mixer to the computer and start Rekordbox. Switch to Performance mode and then choose File -> Preferences.
Under the Audio tab, ensure the mixer is in External mode, and press the Settings Utility button in the left column of the table. In this utility, go to the Mixer Output tab and make sure that all the dropdown boxes underneath Mixer Audio Output are set to REC OUT. Under USB Output Level, choose the desired headroom (I chose -10dB),
Finally, you may have to restart your computer again, or try shutting down the Rekordbox process in the system tray, as this will conflict with Audacity when attempting to record audio from the mixer.