Negative pressure therapy is one of the treatments a wound care center may recommend. It works by pulling the air out of a closed dressing, which creates a vacuum. The negative pressure improves blood flow and pulls out excess fluid.
So there are two mechanisms: blood flow in, excess fluid out.
That also tells you what it looks like, which is the part that tends to surprise people. The dressing is closed, and air is drawn out of it. That is why these dressings are attached to a pump and why they are sealed rather than taped loosely over a wound.
Which wounds it is used for, how long it is used, how often the dressing is changed, and what it feels like are questions for the team using it. They can answer all four for your wound.
What is worth knowing is the company it keeps. Depending on the wound, a wound center may recommend negative pressure therapy, compression stockings, ultrasound, artificial skin, growth factor therapy or skin grafts. A provider may use one or multiple types of dressing as a wound heals. Negative pressure therapy is one option among several rather than a step every wound reaches.