The direction of travel in an orbit is prograde, the opposite direction is retrograde, orbit normal+ is perpendicular to the orbital plane toward the north, normal- is toward the south. If you point your ship directly toward the center of the earth and burn, that would be inward velocity, directly away would be outward velocity. So, when you set up a burn to leave, let's say earth orbit to go to mars, for example, you will likely do a burn that incorporates vectors in all three axes, pro- or retrograde, plane change (normal+, normal-) and inward/outward. Time is the final adjustment, to burn at the right time. The effect is more or less, prograde will certainly allow you to escape earth's gravity, but in regard to the solar portion of the transfer orbit will make the size of the orbit larger, the plane change vector will change the inclination, and the inward/outward will change the eccentricity. Hope that helps.