The planning module is simply a visual representation of the contract. The contract and planning module communicate with eachother in realtime.
If you are more visually inclined, you can start from the planning. Each phase is represented by a block. This allows you to play endlessly according to the evolution of the project. You do this by connecting the phases with the mouse, making them overlap, lengthen or shorten. Every change in a phase automatically translates into a recalculation of the entire project. Subsequent phases are also adjusted.
If you prefer to change the start or end date of a phase in the contract, you can also do this via the contract module.
Because both modules are linked to eachother, you only have to make changes once in the module of your preference