If you are trying to build your chest muscles but not seeing the results you are wanting, there could be several factors at play. First off, your chest muscle is broken up into three sections.
There is the upper section, the middle section, and the lower section. In order to add mass to each section just doing bench presses won’t cut it. To target the upper portion of the pec muscle start on some incline bench presses. Performing the standard press on an incline bench stresses the upper portion of the pectoral muscles thus, helping out your definition in that area.
If you then switch to the decline bench you are going to shift the focus on the lower pec muscle.
Everything is about balance when working out. Developing all areas, all muscles, and all muscle groups. Not only does this lead to better definition on the individual muscles, but it leads to better overall strength.