My left eye is having a problem focusing properly, especially at computer distance. if i cover my right eye the left starts focusing better.?

Blurred vision: Your description sounds like you may be experiencing some dryness and related blurred vision. When the eye is dry, it can make focusing more difficult. I would try some artificial tears and see if it gets better. If it does not resolve or gets worse, then you should go see a doctor for further evaluation.

Blur: From your description this sounds like it could be either a problem with dryness of the surface of the eye, or simply that you need prescription glasses. See your eye doctor to determine which is the problem.