Cardinal Signs
The signs Aries, Cancer, Libra, and Capricorn are in the cardinal mode, and are called cardinal signs.

These cardinal signs are the 1st, 4th, 7th, and 10th signs in the natural zodiacal sequence that starts at Aries. In arc degree terms, they start at 0, 90, 180, and 270 degrees.
Each pair of adjacent signs in the sequence are 90 degrees apart, or what astrologers call in square to each other. So Aries and Cancer are square to each other, and so are the pairs Cancer-Libra, Libra-Capricorn, and Capricorn-Aries.
Also, each pair of signs that are 180 degrees apart are opposite each other. So Aries and Libra are opposite each other, and so are Cancer and Capricorn.
Together, the cardinal signs are said to comprise the cardinal cross.
Cardinal signs are inclined to start things. People whose planets are in cardinal signs like to get things rolling. This initiative is taken in the manner of the element in which the planet is placed. So, for instance, Aries being a fire sign will initiate adventures or actions, just for the sake of it. While Cancer being a water sign will set in motion actions that spring from the emotions, such as initiating contact with family or friends. Capricorn being an earth sign will initiate action toward building things of practical value. Libra, as an air sign, will initiate planning or organizing action geared to social effect.
Fixed Signs
The signs Taurus, Leo, Scorpio, and Aquarius are in. the fixed mode, and are called fixed signs.

These are the 2nd, 5th, 8th, and 11th signs in the natural sign sequence. In arc degree terms, they start at 30, 120, 210, and 300 degrees.
Being 90 degrees apart, Taurus and Leo are square to each other. So are Leo and Scorpio, Scorpio and Aquarius, and Aquarius and Taurus. Also, Taurus and Scorpio are opposite each other, as are Leo and Aquarius. The fixed signs taken as a family make up the fixed cross.
Fixed signs are inclined to maintain things. Fixedness is about stability, so people whose planets are in fixed signs are into doing what it takes to maintain status quo. You want to turn to them to ensure that events once started can keep rolling. There is a fixity or purpose, a willingness to see things through the end no matter the cost.
Each of the signs in the fixed mode will express according to its element. So while Leo’s fixity has to do with a continually burning fiery spirit that is not dampened by adversity, Aquarius’s fixity is seen in the airy world of ideas – plans once adopted are held on to without compromise no matter the opposition. Scorpio, being a water sign, will sustain emotions and feelings long after everyone else has moved on, and earthy Taurus will persevere doggedly in pursuit of material and practical security for as long as it takes.
Mutable Signs
The signs Gemini, Virgo, Sagittarius, and Pisces are in the mutable mode, and are called mutable signs.

Respectively, they are the 3rd, 6th, 9th, and 12th signs in the natural zodiacal sequence. In terms of degrees, they start at 60, 150, 240, and 330 degrees.
Being 90 degrees apart, Gemini and Virgo are square to each other. The pairs Virgo-Sagittarius, Sagittarius-Pisces, and Pisces-Gemini are also square to each other. And with a separation of 180 degrees, Gemini and Sagittarius are opposite each other, and so are Virgo and Pisces. The mutable signs taken together form the mutable cross.
Mutable signs are adaptable – to people, to situations, to ideas. People with planets in mutable mode have a naturally flexible approach to life. The essence of adaptability in mutable signs is the ability to change with times and circumstances. These people dislike dogmatism, and are able to take changes in stride.
The actual area in which such flexibility or adaptability is shown depends on the sign’s element. So, for instance, airy Gemini is flexible in its viewpoint, willing to change perspective according to the information it receives. On the other hand, watery Pisces is flexible in the way it adapts its emotions according to the people or situation at hand, instinctively reacting and adapting as needed. Fiery Sagittarius is open to changing its perspective or belief system according to new knowledge that may become available, while earthy Virgo is nimble and quick to deal with changing practical or material circumstances.