Δv is the ideal change in velocity a rocket can produce. Specific impulse describes how effectively an engine uses propellant; it does not tell you thrust or flame size. Initial mass includes the propellant, spacecraft and payload. Dry mass is what remains after the modeled propellant is used. The mass bar shows the initial composition, not a live fuel level.

Burn 1 moves the spacecraft from its starting circular orbit onto an ellipse. After coasting halfway around that ellipse, burn 2 matches the target circular orbit. Outward transfers add speed; inward transfers reduce it. The displayed Δv adds the magnitudes of both burns. This is an ideal Hohmann transfer, not a guarantee of the best route for every mission.