Description and use:

Red Yellow Cotton Sacred Pooja Doll Thread, Hindu Shudh Dhaga Ritual, Kalawa Moli Religious Ceremony, Mystical Positive Energy Psychic Aura.
The thread is used as a cloth offering to the deity and as a Raksha sutra. The sacred kalawa thread is an integral part of any puja. Mauli dhaga is believed to be a blessing from God and acts as a Raksha sutra that protects the wearer from evil.

It's part of every Hindu ceremony, ritual, or Havan. Moli Kalava is used as an offering to Hindu deities and then worn around the wrist after a ceremony/ritual ends.
Many times, people also use it before the start of the puja ceremony, just after offering it to the Hindu deity.
It is used during and after Pooja and helps to attract all divine powers towards you.
Used on all appropriate occasions.

More symbolism -
Red is the color of fire and blood, so it's associated with energy, strength, power, and determination. Therefore, the red thread has symbolic effects, warding off evil from the person who wears it.
Yellow is associated with joy, happiness and energy.

Tying this sacred thread on the wrist produces a combination of both;
# Ward off evil from the person who wears this red thread.
# To control the mood swings one experiences in daily life.
# To keep the wearer firm in the ritual or ceremony as a reminder on their wrist
# It also reminds you of the importance of who you are and what you stand for.