Interphase is the longest phase of the cell cycle and in which cells will spend most of their life. In this phase, the cells prepares for division through mitosis.
Interphase begins with G1 (also known as Gap 1) in which the cell synthesizes proteins for mitosis. In doing so, the cell's metabolism is sped up, breaking down carbohydrates, and generating energy. In this phase, the daughter chromosomes from the previous phase each have one DNA molecule.
The next stage is called S Phase (also known as Synthesis Phase) in which the cell's DNA is replicated. Each of the DNA molecules are doubled to form two sister chromatids.
The final stage is G2 (Gap 2) where the cell continues to grow, synthesize more proteins, and stocks up energy to prepare for cell division. After G2, the cell finishes with Interphase and moves on to the first stage of mitosis called M Phase.