Tension is the force exerted by a rope on the body,. .

[sweet-buds]

Tension is the force exerted by a rope on the body,

when a rope(massless) connects 2 bodies on a plane, like 2 blocks , which side is direction of tension?
Tension always pulls a body or rope, never pushes the body or rope.

also, r bodies conected with a massless cord assumed to have common acceleration? if yes, why?

 

[rcgldr]

Which side is direction of tension?

Inwards, it's not a side. No matter how small a cross section of rope is examined, the direction of tension is inwards. There is an attractive force trying to pull the molecules of the rope closer together, and the blocks at the ends of the rope are resisting this inwards force.

r bodies conected with a massless cord assumed to have common acceleration?

Not sure what you're getting at here, but only if the blocks are accelerating in a direction that is in line with the cord. One simple example would be to have the center of the cord fixed, while the two blocks "orbit" the center, creating tension equal to mass of one block x v^2 / r. Both blocks would be accelerating "inwards" while orbiting the center. For a linear example, if one block is being accelerated, tension in the cord will cause the other block to accelerate at the same rate, and tension will equal mass of the other block times the rate of acceleration.