A horn clause is a disjunction with at most one positive literal, e.g.
\begin{align}
\lnot X_1 \lor \lnot X_2 \lor \ldots \lor \lnot X_n \lor Y
\end{align}
The implication $X \rightarrow Y$ can be written as disjunction $\lnot X \lor Y$ (proof by truth table). If $X = \lnot X_1 \lor \lnot X_2 \lor \ldots \lor \lnot X_n $, then $\lnot X$ is equivalent to $X_1 \land X_2 \land \ldots \land X_n$ (De Morgan's law). Therefore, the above clause is logically equivalent to
\begin{align}
(X_1 \land X_2 \land \ldots X_n) \rightarrow Y
\end{align}
A Prolog program basically is a (large) list of horn clauses. A Prolog clause (called rule) is of the form
head :- tail.,
which in logic notation is $head \leftarrow tail$. Therfore, any horn clause
\begin{align}
\lnot X_1 \lor \lnot X_2 \lor \ldots \lor \lnot X_n \lor Y
\end{align}
is written in Prolog notation as Y :- X1, X2, X3, ..., Xn.
A horn clause containing no positive literal , e.g. $\lnot X_1 \lor \lnot X_2 \lor \ldots \lor \lnot X_n$ can be rewritten as $(X_1 \land X_2 \land \ldots X_n) \rightarrow \bot$, which is :- X1, X2, X3, ..., Xn. in Prolog notation.
Regarding your examples:
- "John is beautiful and rich", is a CNF, and each clause contains at most one positive literal, hence it can be written in Prolog as
beautiful(john). and rich(john).
$\forall X \ \exists Y \ \operatorname{Loves}(X,Y)$
That nested extential quantifier can be eleminated by Skolemization, which is introducing a new function for the extential quantifier inside the universal quantifier: $\forall X \ \operatorname{Loves}(X,p(x))$, which in Prolog notation is loves(X,p(X)).
