  In this paper, we discuss various basic properties of moduli of smoothness of
functions from $L_p(\mathbb{R}^d)$, $0<p\le \infty$. In particular, complete
versions of Jackson-, Marchaud-, and Ulyanov-type inequalities are given for
the whole range of $p$. Moreover, equivalences between moduli of smoothness and
the corresponding $K$-functionals and the realization concept are proved.
