What is a Tabernacle Used for in the Catholic Church?

I often like to pray in front of the Tabernacle.  My wandering is less when I'm looking at a Tabernacle.  In fact, once when I was on my Cursillo at St. Basil's in Methuen, MA, I took my pillow and blanket, and went up to the third floor altar and slept in front of Jesus, on the carpeted floor in front of the altar.  St. Basil's is staffed by the Melkite Greek Catholic Order of priests.  I use to babysit the pastor, Father Martin Hyatt.

Let me explain.  I come from Methuen, MA.  I went to high school right next door to St. Basil's Seminary. (Presentation of Mary Academy)  I grew to love the Salvatorian Fathers.  Father Martin Hyatt comes from Methuen, also.  That's how I came to know him.  

I wish I had my camera with me on that Cursillo.  The Melkite Greek's communion hosts are little cut up pieces of bread.  They are kept in a covered chalice.  It was placed in the center of the altar, where I slept.   

What is a Tabernacle? 

In the "General Instruction of the Roman Missal," under "The Place for the Reservation of the Most Holy Eucharist", we read:

314. In accordance with the structure of each church and legitimate local customs, the Most Blessed Sacrament should be reserved in a tabernacle in a part of the church that is truly noble, prominent, readily visible, beautifully decorated, and suitable for prayer.

The one tabernacle should be immovable, be made of solid and inviolable material that is not transparent, and be locked in such a way that the danger of profanation is prevented to the greatest extent possible. Moreover, it is appropriate that, before it is put into liturgical use, it be blessed according to the rite described in the Roman Ritual.

315. It is more in keeping with the meaning of the sign that the tabernacle in which the Most Holy Eucharist is reserved not be on an altar on which Mass is celebrated. Consequently, it is preferable that the tabernacle be located, according to the judgement of the Diocesan Bishop,

a. either in the sanctuary, apart from the altar of celebration, in a form and place more appropriate, not excluding on an old altar no longer used for celebration;

b. or even in some chapel suitable for the faithful’s private adoration and prayer and which is organically connected to the church and readily visible to the Christian faithful.

316. In accordance with traditional custom, near the tabernacle a special lamp, fuelled by oil or wax, should be kept alight to indicate and honour the presence of Christ.

Tabernacles have generally been made of metal (such as bronze or brass), or sometimes of heavy wood. They are traditionally lined in white cloth (often silk), and are always securely lockable and generally permanently affixed or bolted to their support. Some Tabernacles are veiled when the Eucharist is actually present in them. These veils are often of cloth and design similar to the priest's vestments (that is, to create a harmony of design), and are either white (the color of the Eucharist), gold (which may be substituted for white), or of violet, green or red depending on the liturgical color of the day or season.

[Source: http://en.wikipedia.org/wiki/Church_tabernacle]

In summary, the Tabernacle is the place where the Real Presence of Jesus dwells within the catholic Church. While the Consecrated Host has the appearance of Bread, It is the true Body of Jesus living among us in fulfillment of God's promise during the days of the Old Testament to come and make His dwelling among His people.

And here are some examples:

Tabernacle inside the chapel inside St.Thomas Aquinas' Priory at Providence College.  

Tablenacle in Guest House
St. Joseph's Abbey
Spencer, MA

St. Mary's Church
Franklin, MA