A birth chart isn't just planets and signs — it's also divided into twelve houses, each representing a life area. The same planet lands differently depending on which house it's in: Mars in your 1st house behaves differently than Mars in your 7th.
Quick reference: 1st is identity and first impressions, 2nd is money and self-worth, 3rd is communication, 4th is home and family, 5th is romance and creativity, 6th is health and daily routine, 7th is partnerships, 8th is intimacy and transformation, 9th is beliefs and travel, 10th is career and reputation, 11th is friendships and community, 12th is the subconscious and endings.
Houses are why two people can share a Sun sign and feel completely different to be around — the placements filling their houses are doing most of the actual work. Bookmark this one. Every other astrology piece on this site assumes you know roughly what a house is, and this is the fastest way to get there.