A still air box or ‘SAB’ for short, is simply an upside down plastic storage box/tote with 2 holes cut out of the sides for your hands to go into, allowing you to work inside the plastic box/tote.
This creates an environment with very little air flow inside, reducing the chance of airborne contamination from the larger room. These can be a little bit tricky to work inside, as you can be limited for space to move inside the box.
A step up from an SAB, is something called a laminar flow hood.