Yes I do believe in astrology .. not so much the western astrology but the Indian one ..
This is what my understanding is –
it takes into account your date of birth, place of birth(longitude & latitude) and time of birth. According to the date, time and place u were born and the position of planet at during ur birth determines ur rasi (start sign) and certain (general) things about u .. like ur characteristics .. lucky numbers, lucky stones, lucky/unlucky days of the week .. also a range of dates where u may face good times/bad times, that too according to the position of the planets.
Some of u may have heard ppl saying things like – they are similar becoz they belong to the same rasi/star sign or u are facing a bad time/good time according to ur birth chart (kundali) .. like they have a garah
Why do ppl compare gal/boy horoscopes b4 marriage .. this is to see if they are compatible or not .. there are comparisons of 36 different aspects .. it is called 36 gun milap .. it will state in which areas the boy/gal are compatible and which areas they aren't and then the total out of 36 is determined to score the match.
What I have written above is what I know from what I have been told by family/pundits and from my own experiences.