To measure diffusion coefficients, either Fluorescence Correlation Spectroscopy (FCS), Fluorescence Revovery After Photobleaching (FRAP), Fluorescence Loss In Photobleaching (FLIP) or Photoactivation can be used. Often these techniques complement each other. Additional information found using FCS is the molecular concentration and with FRAP you will obtain the fraction of mobile and immobile molecules. These techniques, except for FCS, can be used to visualize how the fluorescent molecules move in a cell.
To study binding and molecular interactions, on a scale much smaller than the optical resolution, Fluorescence Cross Correlation Spectroscopy (FCCS) or Fluorescence Resonance Energy Transfer can be used.