Mercury is just over a third as far from the sun as the Earth is; it is 0.387 A.U. from the sun (on average). Mercury's orbit is very eccentric; at aphelion (the point in the orbit farthest from the sun) Mercury is 70 million km from the sun, at perihelion Mercury is 46 million km from the sun.
There are no seasons on Mercury. Seasons are caused by the tilt of the axis relative to the planet's orbit. Since Mercury's axis is directly perpendicular to its motion (not tilted), it has no seasons.