In astrological tradition, the Mars governs drive, desire, and the way energy is asserted, while Gemini is a air sign read as curious, quick, versatile, and talkative.
So Mars in Gemini is often read as a placement where how someone goes after what they want and meets conflict takes on a curious, quick quality. Tradition holds that someone with this placement tends to pursues and takes action in a way that feels versatile — coloured by the air-sign temperament of Gemini rather than by any single rule.
None of this is a prediction or a fixed trait. These are tendencies astrologers have long associated with Mars in Gemini, and how they actually show up depends on the rest of the chart — the houses, the aspects, and the other placements that this guide cannot see.
A general guide to astrological tradition — tendencies, not predictions. It describes the placement in the abstract and is not about any specific person.