Fluid mechanics is the study of how fluids (liquids and gases) behave and interact with forces. It involves understanding concepts like pressure, buoyancy, and flow.
Viscosity is a measure of a fluid's resistance to flow. It describes how "thick" or "sticky" a fluid is, and it depends on the internal friction between its particles.
Pressure is the force exerted per unit area on an object by a fluid. It can be thought of as the "push" that fluids apply on surfaces they come into contact with.