Floorplanning vs Placement in VLSI
Floor planning can be considered your top level design and it may for example be guided by pin placement or interference between different modules. It is sensible to think about the overall design here; you may not want to place a sensitive analog component directly next to an RF oscillator.

Placement is then putting the gates within the overall plan. This may be fine first time round for a simple design, but it could be that your original floor plan does not, for example, allow all timing constraints to be met. 

All the steps are related, so think of planning and placement as different levels of abstraction. It is usual to iterate through a number of designs to reach closure on all area and timing constraints.