That’s super simple.
Double tap a track button, press left arrow which brings you to the screen where you load a machine into a track.
Choose Flex Machine for short samples (ram playback), or Static Machine for playing longer samples (streaming from cf card).
Flex and Static Machines each have a slot list with 127 samples (the first 8 on Flex Machines are the Track Recorder, that can play back audio you sample/sampled).
Double tapping a track button brings you to the sample slot list. The sample slot list can be populated with samples from the cf card.
If you loaded a view samples into the sample slit list, highlight one with arrow keys up/down and press yes to assign it to the tracks machine.
Read the pdf manual, really. Do it.
Also read Merlins Guide and Elektron Music Production Tips by Olaf Wolkenhauer
You might find this List of OT Button Combinations handy.