Can anyone explain to how where stars and planets are have anything at all to do with your personality? I'm very confused upon how these conclusions are drawn and I don't understand how it could help me "understand" anything about myself any better. I feel like there's something I'm missing here, can someone explain the actual science of all this?
I experienced the same type of confusion when first learning astrology as well/ So i really feel you on this. But here is a breakdown of the METHOD that most intermediate or advanced astrologers rely on. I will not get into what the exact definitions of planets, signs, etc mean...but i will try to give a very basic overview. I am no expert and I am still learning.
First learn the difference between the planets (the Sun, Mercury, Pluto) and signs (Aries, Scorpio, etc).
The planets are the WHAT of any chart. For example ; Mercury deals with communication to be very simple.
The signs are HOW the planets are expressed in the chart. If Mercury the planet of communication is in your Libra - then your communication style will be expressed through diplomacy, fairness, judicial balance, mediation, etc because Libra is a sign of diplomacy, etc. If Mercury was found in Scorpio lets say then your communication will be more intense, with few strong words, powerful, maybe even intimidating, kind of communication people will take notice.
The House ( which a House system is divided into 12 houses - each representing an area of your life) - Is the WHERE all this planet/sign combo will manifest. Continuing the above example; lets say Mercury in Libra fall in your 6th house. 6th house represents daily chores, work, dealing with minor relationships, work related, minor work we do day to day to survive. In this case; Mercury in Libra will manifest in your life specifically in areas of your daily work, chores, responsibilities. This can mean that you deal with people in a diplomatic and fair manner and as a result of this placement you may find yourself working in jobs that require you to use this skill. Working in customer service, travel agent, etc.
This is the basic Method. To move forward after the basics: Things get even hairy when you add aspects to iy. Aspects are simply the geometric linkage between planets. The aspects run like basic geometry you have planets making 90 degree angle, 180 angle, etc. Each aspect has a specific nature or quality to it. Each angle/aspect is also regarded as challenging, harmonious or slightly difficult and so on. ASPECTS always color or alter the planet it is making an aspect with. For example: you may have Mercury conjunct (0 degrees) Uranus. Uranus is a planet of unexpected, rebelliousness, out of the ordinary, unstable, etc. This combo could result in your communication style to be spontaneous, out of the ordinary or unusual that draws people attention. Or you use your communication to fight against unfair authority, etc.
Progressions will give you insight on what is going on right now. Planets are always moving. Learning about the faster moving planets like the Moon, Venus, Mercury versus slow moving outer planets like Pluto, Uranus, etc also gives you insight into your psychological nature.
There is so much more to learn and study. I find it more complex and interesting than MBTI. You can dig and dig and gain understanding on yourself that only you will figure out. But i admit it is not easy in the beginning. I recommend books over websites if one is very serious. The ultimate goal of being an astrologer is to be intuitive reader, not following an already written script.