I thought seasons changed with revolution of earth around Sun on its orbit and day/night by rotation?

Seasons aren't actually based on our distance from the sun (which is roughly constant) but by the tilt of Earth's axis of rotation relative to the sun. Imagine a tennis ball with a pencil through the middle which is then stood on end. Earth rotates around a central axis (the pencil) but this axis is not perpendicular to the sun (the pencil leans to one side). The rotational axis always leans to the same side, however, so as the year goes by and the Earth moves around the sun, a different hemisphere (northern or southern) gets more or less sunlight per day. (If you have a tennis ball, pencil, and a lamp you can demonstrate this by holding the pencil at an angle and seeing how the light shifts as you move the ball around the lamp.) Take a look at the Wikipedia page for pictures.

The axis of the earth doesn't point straight up, it is tilted. This means that in July (for example) the northern hemisphere is pointing towards the sun, and in January it is pointing away from the sun. The southern hemisphere obviously points in the opoosite direction, so that is why Australia has summer in December. It is the same for any temperate country south of the equator. This also explains why the Artic circle has permanent night for months during winter and permanent day in the summer.

The earth tilts on its axis. When the Northern Hemisphere is closer to the sun, it is summer there, and winter in Australia, and vice versa.

You have to take into account the earth's tilt

p.s. half way round the sun its tilting away from the sun

The seasons are caused by tilt, if it wasn't tilted, the orbit would not change the seasons.