What is barbell complexes? I imagine oly type lifts?
No, they're a conditioning exercise.
As I do them, you just take a bar, and you just randomly pick barbell exercises that you can do, doing 10 reps of each, fastish, then moving to the next one. And you do them for time, e.g. do them for 2 minutes, 3 minutes, whatever. So today, my first two minutes, I think I did 10 front squats, then 10 OHPs, then 10 hang cleans, then 10 bicep curls... then something else, I can't remember. That was 2 minutes. Then a rest, then I did another 2 minutes... 10 deadlifts, 10 Bent Over Rows, 10 back squats, 10 overhead presses, etc. Because it's a conditioning exercise, you're not trying to lift heavy weight, you're trying to go at a fastish pace without stopping, doing something that is reasonably hard.
Once it gets easy, you can go for longer, take shorter rests or start adding more weight. But it should never get heavy- it's conditioning and muscular endurance, not strength.
I didn't do them for long, and they really tired me out. I was super-lame.