Mars, the red planet, has typically been associate with war. The God Mars was a skilled and sought-after warrior.
In astrology though, Mars stands for our instinctual masculine qualities. Mars signifies the way in which we assert ourselves to attain what we want. It is a part of ourselves that acts upon the world without much thinking or decision making. Mars just acts.
We associate the planet Mars with the sign of Aries - the first sign of Spring. In the beginning of Spring, the seeds sprout bravely and push their way through the surface of the soil. Mars likes to be brave and Mars likes to move quickly. For example, if Mars is in the first house, that person will tend to rush into situations without thinking about whether they are appropriate for them, whereas Mars in the seventh house will rush into committed relationships - for better or for worse. Mars in the fourth house will be quick to retreat into their home, where they might rush about tidying to burn off energy. Mars in the tenth house will take rapid steps towards building their ideal career.
I like to tell my clients that wherever they have Mars in their chart, they have “rocket fuel” and that is an area of their life they can cultivate results quickly - though they must be wary of jumping before they leap.
Mars relates to our sexuality too and often Mars in our chart will indicate lust. Unlike Venus who seeks to attract, Mars takes the leap and goes after what it wants.