What's the difference between P = FV and P = FS? I don't know which one to use most of the time

What's the difference between P = FV and P = FS? I don't know which one to use most of the time

FS is the work done by the force, not the power. FV is the power
The formula is p = FV and w = FS

The formula ρ = MV is defined by the ratio of m to v. there are similar formulas___ ．

Density is the amount of material contained in a unit volume, which is defined by the ratio of mass to volume, with the definition formula of ρ = MV; speed is the amount of distance per unit time, which is defined by the ratio of distance to time, with the definition formula of V = st; pressure is the pressure on the unit area, which is defined by the ratio of pressure to stressed area The definition formula is p = FS; power is the work done by an object in unit time, which is defined by the ratio of work to work time, and the definition formula is p = wt. so the answer is: v = St

From the formula P = m / V, P is proportional to m and inversely proportional to V, right?

It seems wrong
The density of a definite substance in a definite state is a definite quantity, which is its inherent property different from other substances and does not change with the change of weight and volume
The density of a substance can be obtained by the formula P = m / v
But for a given substance, if M changes, then V changes. In fact, P does not change