After a temple is built the church has an openhouse for anyone who wants to see it. There are tours held. This usually lasts several weeks. After the open house is done, the church prepares (i.e. cleans, vacuums, final prep work, etc. ) the temple to be dedicated. The temple is then dedicated usually by the Prophet of the Church. After a temple is dedicated then only worthy members of the Church are allowed inside. Here is a place to find out about temples: http://www.lds.org/temples/purpose/0,11298,1897-1,00.html 
 
A worthy member means they have had an interview with their Bishop. The Bishop is responsible for ascertaining whether a member is worthy or not. Worthy means they are keeping the basic commandments (Word of Wisdom, Chastity, Tithing, etc.), they attend church regularly and are serving in the church (this might be teaching a youth Sunday School Class, etc.). 
 
It is a great blessing to attend the temple and to feel the Lord's Spirit and the peace found there. In essence the temple is a bit of heaven on earth.