The Blessed Sacrament refers to a consecrated host. If the Blessed Sacrament is exposed, then the priest has put it in a special “container” in which the host can be seen, called a “monstrance.”
When people come to visit the exposed Blessed Sacrament, we call that Adoration. We adore Christ in the visible Blessed Sacrament; He is present Body, Blood, Soul, and Divinity under the appearance of bread, as seen in the monstrance.
When the Blessed Sacrament is not exposed, which is most of the time unless your parish has a separate 24-hour adoration chapel, it is stored in the tabernacle. Anyone is welcome to come to church at any time and pray before Christ in the tabernacle. You can’t see the Blessed Sacrament since it’s inside the tabernacle, but Christ is still there, Body, Blood, Soul, and Divinity in the tabernacle. That’s what the red tabernacle candle signifies, that consecrated hosts, the Real Presence of Christ, is in the tabernacle.
Anyone and everyone is welcome to pray before the Real Presence of Christ in the tabernacle or exposed in a monstrance.