The sunlight is moving away from sun.Venus comes first, then earth.?

The sail is not a part of the Akatsuki probe, it is part of the IKAROS space craft, just one of the five other missions launched at the same time, on the same rocket as the Akatsuki probe. It is a test of whether a solar sail is as viable a propulsive method as many believe it could be.

Basically the sail is expected to work just like a regular sail on a boat, except that instead of the wind blowing on it, there is light from the sun reflecting off it and imparting momentum to the satellite (as the particles of light, called photons, have some momentum). The sail can be used when falling towards the sun to lose energy, or when travelling away from the sun to gain energy.

Such a method will work best in a highly elliptical orbit around the sun, and it will also work much more effectively when closer to the sun.

There are also techniques where varying the angle of the sail relative to the sun could allow for some modifications of orbits around the inner planets, possibly to compensate for a lower than planned orbit after launch or to provide some maneuverability in orbit.

Additionally this could be very important for lowering the mass, and hence launch costs of missions, improving the useful life of the satellites, enabling safer and more reliable de-orbiting options at the end-of-mission time, removing the need to carry volatile chemicals to orbit onboard the satellites for fuel, and many other benefits besides.

Edit: Martin, I can't seem to find anything about IKAROS having an ion drive, only the solar sail. Do you have a source for that? The only mention of an ion drive I can find is in future plans for a more advanced mission if IKAROS proves the concepts work.

The launch of AKATSUKI included several piggyback payloads on the same rocket. The one you're interested in is IKAROS, a solar-sail experiment. IKAROS will use its sail both for propulsion and as a solar panel to generate electrical power, some of which will go to a low thrust ion engine. In other words, it'll have two ways of propelling itself which will work together.

The way the sail can be used to navigate inward, closer to the Sun, is by tilting the sail at an angle whereby the light radiation will bounce off strongly in the forward direction. As it does the spacecraft will be slowed down a bit. By being slowed, it loses orbital energy and its path curves closer to the Sun. By doing this in a careful, exact manner, it can be navigated to the planet Venus.