When two planets sit within about 8° of each other, they conjoin — they act as one blended thing, for better or worse.
A sextile (60°) is a helpful hand-off between two planets. The energy is available — but only if you notice and use it.
A square (90°) is a hard aspect — two planets in the same modality but different elements, pulling against each other. The friction is the point.
A trine (120°) is a natural flow between two planets in the same element. Talent lives here — sometimes so freely it goes unused.
An opposition (180°) is a face-off between two planets across the chart. You see one; the other you tend to project onto other people.
A quincunx (150°) links two planets that share nothing — different element, different modality. The result is a chronic awkward-hip.
A semisextile (30°) is a small, subtle connection between adjacent signs. Not loud, but persistent.