Vakra tunda mahakaay; surya koti samaprabhah |
Nirvighnam kuru me deva; sarva karyeshu sarvada ||
 
Lord Ganesha is the God of knowledge and intellect. These above lines are chanted while worshiping him which means O my Lord Ganesha of curved trunk, large body and the brilliance of million suns you have,please make my work free of all obstacles always.

He is the Vighnaharta or the destroyer of all obstacles.Lord Ganesha is worshiped before the commencement of almost every task.He is worshiped first in almost all rituals of Hinduism. 

Not only he is the destroyer of all obstacles; he also gives you success. He is worshiped for obstacles like failure in life, obstacles in marriage etc.