Wireless sensor network composed of infrastructureless, small, low-power, low cost, dynamic nature, application oriented, and multihoping wireless nodes, design for the purpose of collecting information by environment sensing, processing and communication. Designing of these networks become more complicated due to deploy nodes characterstics, maintenance of database, security, authentication and its functioning in open environment. This paper presents a general overview of WSN in detail and covers its applications and vulnerable aspects of WSN.