That is possibly the most asked question in Astrology lol. It is a craft with such a bewildering array of details and a myriad of methods and avenues of interpretation to explore, that it is virtually neverending in where your investigations might take you to find meaning.
However, briefly, the Sun, Moon and Ascendant are the three most deeply personal of positions to consider in a birthchart. The sign of your Sun is Pisces. When you say my star sign or zodiac sign is Pisces it is because when you were born that is physically where the Sun was (be still siderealists).
Yes, there is now a great deal of variation in approaches in Astrology, such that the beginner can become very confused.
The dominant approach for the last 50 years has been a psychological one. That sees the birth chart as being a map of your psychology - everying in it relates to who you are and what you do. It's a mind map.
I follow a more traditional approach, so while I agree with zhan.thay on the primacy of the trinity of Ascendant, Sun and Moon, I take a slightly different slant. to them. Traditionally the Ascendant is you. the physical body that you have during your life time and a general indicator of your 'Mind, and Body Spirit. The rest of the chart, says something about your place in the real world, your family, partner, how you act at a social level (including your career) and where you have both strengths and weaknesses in dealing with that outside world.
If the Ascendant is the physical you, The Sun is your will, what one might term directed action. How you impact on the world and on others. This gives it a mental, and a physical role. Your ability to influence things around you and what used to be called your higher mind.
The Moon too has meaning both at a physical and mental level. physically it has meaning for your body and it's health and well being. At a mental level it's your intuitive or reactive mind = what used to be called your animal mind. The Moon shows your instinctive reaction to situations, where there is no time to think.
There's at least one other important signifcator, the ruler of your Ascendant, as that act as the steering force to guide you through your life. In your case it's Jupiter, ruler of Sagittarius.
To extend your knowledge you need firstly to learn what the planets signify (and planets are multi faceted, they have several meanings and those meaning can vary according to context), secondly you haveto realise that the signs show the natural strength or weakness of the planets within them. how good the actors are in their place. planets tend to be stronger in some signs than others. Thirdly, Then you need to look at the twelve houses and begin to understand what they signify. Once you have got that idea, the thing is to try and work out what a planet means when it's in a house, working on how strong or weak it is and what area of life that the house signifes. to get some idea of how that planet manifests in your life.
Lastly you look for connections between planets - aspects - to see if they enhance the planets concerned or whether they weaken them. It's not an easy process. When I learned I ended up with sheets and sheets of paper and tried to make sense of my scribilings. But if you keep to those three principles of planets (the actors), the Signs (their strength of weaknesses) and the houses (where they influence your life). You will begin to make sense.
Incidently, as you will find a host of different variations, especially on houses, it's always best to give your natal details as d.o.b. time of birth and place of birth. Then members can erect your chart using their preferred methods.