One way to explain how the different organelles in a cell operate is to think of the cell as a miniature society. Within its walls are factories, power plants, a leader, a packaging plant, a central gathering place and recycling stations. All work together to sustain the community.
The cell is protected by its outer boundary, the plasma membrane. Like a gated community, the cell has security guards that control what molecules are allowed to enter and leave the cell.
The ribosomes are the small factories of the cell. They float throughout the cytoplasm and create proteins. The endoplasmic reticulum is the big factory complex, and it too manufactures proteins. Some of these proteins are kept within the cell and turned into ATP by the mitochondria, the cell's power plants. Others are transported to the golgi apparatus.
The golgi apparatus is the packaging plant. It separates lipids and proteins and packages them in vesicles, or packets. The type of packet determines if the material will stay within the cell or be shipped out. The lysosomes and peroxisomes are the recycling stations that break down and ship waste out of the cell.
The nucleus is the leader, directing most of what goes on in the cell. It holds the DNA, or the construction plans needed to produce the same type of cells.