  We provide new values for the model parameters of the covariant constituent
quark model (with built--in infrared confinement) in the meson sector by a fit
to the leptonic decay constants and a number of electromagnetic decays. We then
evaluate, in a parameter free way, the form factors of the $B(B_s)\to
P(V)$-transitions in the full kinematical region of momentum transfer. As an
application of our results we calculate the widths of the nonleptonic
$B_s$-decays into $D_s^- D_s^+,$ $D_s^{\ast\,-} D_s^{+}+D_s^- D_s^{\ast\,+}$
and $D_s^{\ast\,-} D_s^{\ast\,+}$. These modes give the largest contribution to
$\Delta\Gamma$ for the $B_s-\bar B_s$ system. We also treat the nonleptonic
decay $B_{s}\to\Jpsi\phi$. Although this mode is color suppressed this decay
has important implications for the search of possible CP-violating New Physics
effects in $B_s-\bar B_s$ mixing.
