Mitosis and the cell cycle. DNA is replicated and this takes place during interphase.

After a cell is created it goes through a several stages:

1. G1: the first phase of growing, when proteins and organelles are being made
2. S: synthesis, when DNA is being replicated
3. G2: the second phase of growth when organelles and energy supplies are increased
4. Prophase: chromosomes become visible, nuclear envelope and nucleolus disintegrate
5. Metaphase: chromosomes line up in the middle of the cell; spindle fibres form
6. Anaphase: Spindle fibres contract pulling chromosomes to the poles
7. Telophase: nuclear envelopes and nucleoli form around both sets of DNA
8. Cytokinesis: the cells cytoplasm divides into two

1, 2, and 3 are all part of the 'interphase' when the cell is not in the process of replicating.

4, 5, 6 and 7 are all part of mitosis, which is explained in greater detail in the following post:

This diagram represents the cell cycle:

(ignore the check point markings)

ricochetscience.com