Who are this people in white, often attend to monks?
He is probably an anagarika.

Anagarika, literally "homeless one", is a stage of practice between lay followers (upasaka) and novice monks (samanera). They usually wear white and act as part time or full time volunteers at monasteries or temples.

They observe the Eight Precepts and are able to handle money unlike novice monks and fully ordained monks (bhikkhu).