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Using results of direct numerical stimulation we have analyzed nonlinear energy transfer between scales of motion in isotropic and homogeneous shear turbulence in both spectral and physical space representation. In all cases we find that the transfer is local, occurring between similar scales, but is always moderated by scales from the energy containing range (local transfer through nonlocal triad interaction). Such local energy exchanges dominate also subgrid-scale energy transfer which was found to be composed as a forward and an inverse transfer components, both being significant in dynamics of large scales. The spatial structure of the subgrid-scale transfer was compared with the structure of a number of physical quantities which are considered important in the dynamics of large scales giving usually poor correlations. Moderate correlations were observed only for the large scale energy and the Smagorinsky's transfer. Finally, a new theory of spectral energy dynamics was developed. The theory provides a plausible physical mechanism of the observed transfer process and predicts the energy spectrum in the inertial and the dissipation range in agreement with experiments and simulations.