I am doing meditation for few months.I see a square or rectangle in third eye, some times a vague figure like a negative.
It’s common to see colors in various shapes when the eyes are closed, regardless of whether one meditates. Sometimes they are like photographic negatives, which can be optical after-images of things we have looked at earlier with eyes open (picture frames, windows, clocks, etc.). Other times they can be vague — or even not-so-vague — images from the subconscious mind. Still other times, they can simply be patterns of light and dark without recognizable shape or meaning.
Those images can also, however, be precursors of the spiritual eye, which is a ring of gold surrounding a field of deep blue, in the center of which is a five-pointed, silvery-white star. When you see the spiritual eye clearly, it will be very distinct. Up until that time, it can be a splotch or a doughnut shape of any color. Let the true vision of the spiritual eye come in its own time — as it likely will, once the mind is very, very calm.
In any case, practice your meditation technique with the aim of that deep calmness (or some other divine quality), not with the aim of seeing a particular image. Spiritual success is not measured by what you see in meditation. Measure your success, rather, by whether you are becoming a happier, kinder person, and whether your devotion to God is growing.
Blessings on your practice,