What do all the variables stand for?

Vo stands for Velocity Original. Typically it's given in questions as some starting speed. If an object's starting velocity is called "rest", then Vo = zero. If the problem talks about dropping an object, then the Vo would be zero because the object initially had no downward motion.

Vf stands for Velocity Final.Given as some ending speed... EX: A car starts from rest and later crosses a finish line moving at 30m/s. In this case, Vf = 30m/s and Vo = 0m/s.

Xo & Xf stand for position original and position final. It is often useful to pick one direction as positive and let the other be negative. EX: If a cliff is 200m tall and we want to know how far something has fallen, we can say that the cliff is +200m and any motion downward is negative. Otherwise, you may solve the problem and say that the object actually fell up! So the equation Xf=Xo+Vot+at^2/2 becomes Xf=Xo+Vot-at^2/2.

If the object were thrown downward, the "Vot" term would be negative too. If it were thrown upward, the "Vot" term would remain positive.

DX stands for change in position. It is often seen in questions as "how far" something has gone.