It is the festival of colors.
Holikas are raw gram crop. So it is celebrated in the month when that crop is ready for reap that is in Phalgun (Feb-March). Phagun is called the month of colors.
People throw colors on each other and enjoy festivities.
Ho-li also means "to end".
The festival is celebrated to generate the feeling that since the Spring has come so let the past differences be forgotten and start the new year with new warmth and vigour to have better brotherhood.