The Holy Ark (Aron Kodesh), where the Torah Scrolls are kept, is situated in the front of the synagogue. The Ark is the holiest place in the Synagogue.
In most synagogues the Holy Ark is on the Eastern wall, so that when we face the ark, we are facing the holy city of Jerusalem, where the Holy Temple once stood.
The curtain that covers the ark is called the Parochet. It symbolizes the curtain that was in the Holy Temple. As it is written (Exodus 40:21), "He brought the ark into the Tabernacle and placed the screening dividing curtain so that it formed a protective covering before the Ark..."
The ark is only opened during special prayers and when removing the Torah to read during prayer services.