Question

why do we receive
rainfall Southwest monsoon from June to September

Answer 1

The pressure and wind conditions over India are unique. during winter, there is a high pressure area north of the Himalayas. cold dry winds blow from this region to the low pressure areas over the oceans to the south.in summer, a low - pressure area devolopes over interior asia as well as over northe west India. this causes a complete reversalof the direction of winds during summer. air moves from the high pressure area over the southern Indian ocean, in a south easterly direction, crosses the equator, and turns right towards the low pressure areas over the Indian subcontinent. these are known as the southwest monsoon winds.
HOPE IT'S HELPFUL DEAR.

Answer 2

The main reason is air pressure. During winter low pressure develops over India due to this winds in high pressure area i.e. S.W. of India moves towards N.E.
Second biggest reason is Coriolis Effect:
You might have Studied that winds and ocean currents deflects towards right in Northern Hemisphere and towards left in southern Hemisphere.

So you got the answer.