Δ is used to mean a change in something, so
Change in Ep = Change in Ek + W
Beyond that I'm stuck unless the person who composed the formula tells me.
I could guess the E stood for energy and the subscripts p and k stood for potential and kinetic.
W might then stand for work.
But that is a total guess, since formulae are made up by people according to their own mathematical needs. An equation or formula without context has no definite physical meaning.
Edit 3. Oh, you asked about use. If it is something like the meaning I guessed, then you might use it to calculate changes in potential energy and kinetic energy when work is done on a body. But you'd have to be very careful to measure the variables suitably, as this formula would not take account of the signs of the quantities. A better formula to use might be ΔPE = W - ΔKE