Experiments and Brownian dynamics simulations have been coupled in order to better understand structural and dynamical properties of ferrofluids, especially the role of the magnetic dipolar interaction. The ferrofluid used is a 'home-made' well defined suspension, the experimental characteristics of which are introduced in the modelled system. In this system, the determination of the structure using simulations and small angle neutron scattering (SANS) experiments shows no sign of chaining in the suspensions, both without and with a magnetic field. Nevertheless, on the scale of the interparticle distance, the structure is strongly anisotropic. This is at contrast with the weak anisotropy of the translational diffusion coefficient under magnetic field on the same scale. Moreover, on the macroscopic scale, both structure and translational dynamics are strongly anisotropic. Also the rotational diffusion is strongly modified if determined without field or after a weak orientation of the particles with a weak field. These results all emphasize the role of the collective phenomena associated with the dipolar interaction.