(Probably not the most “scientifically correct” accurate way to describe) but simply the Valsalva maneuver is taking a deep inhale before you initiate a rep and holding that breath through the duration of the rep. Typically this maneuver gives your back more support while lifting.
Holding your breath during strain has a downside though. It can up your blood pressure quite a bit. If you’re nervous holding your breath during lifts … try engaging the abdominal muscles while lifting to support your middle!