The significator is a card that represents you, the querent, in a tarot reading. You do not have to have one assigned to you. You can pick your significator card for yourself. There is no right or wrong card, your significator card is what you feel helps you bring your energy to the reading. There are different approaches you can take to find the card you feel best suits you. One of the most common methods is to turn to your Zodiac chart. Each suit in the Tarot represents a different element, use your astrological sign to narrow down your choices to a suit. Then choose the card you feel most drawn to.
Those who fall under the houses of Taurus, Virgo, and Capricorn should select a significator from the Suit of Pentacles as this suit represents earth.
People born under Gemini, Libra, and Aquarius should choose a card from the Suit of Swords as it represents air.
If you are an Aries, Leo, or Sagittarius then your suit is the Suit of Wands which represents fire.
The Suit of cups represents water, so if you are a Cancer, Scorpio, or Pisces you would select from this suit.
You can also go a step farther into personalizing your selection by adding your gender to your significator card. To do this you would select a court card in the appropriate suit. If you are a female then you would choose either a page or a queen. For males, you would select either the knights or kings. Many people find this to be the most powerful and significant way to identify with their significator card. If you do not feel an attachment to any of the cards in your suit there are other methods like letting the cards choose you in which to determine your significator.
To do that you would clear your mind, relax, and then shuffle the deck while focusing on finding your perfect significator. When you feel you should stop then stop shuffling. Spread the deck out face down in front of you and select a card at random.