Proposition 13 in Royden's Real Analysis According to the Proposition 13 Ch.1 in the book Real Analysis by Royden:

Let $F$ be a collection of subsets of a set $X$. Then the intersection $A$ of all σ-algebras of subsets of $X$ that contain $F$ is a σ-algebra that contains $F$. Moreover, it is the smallest σ-algebra of subsets of $X$ that contains $F$ in the sense that any σ-algebra that contains $F$ also contains $A$.

I don't understand what this theorem says at all, especially there are many "contain"s and I am confused. Maybe because I am not a native speaker..
Please help! 

Mathematical "translation":

Let $F\subset2^{X}$. Let $\mathcal{B}$ be the set of all $\sigma$-algebras $B$ on $X$ such that $F\subset B$. Then, $A=\cap_{B\in\mathcal{B}}B$ is a $\sigma$-algebra such that $F\subset A$. Moreover, for any $\sigma$-algebra $A^{\prime}$ on $X$ such that $F\subset A^{\prime}$, $A\subset A^{\prime}$.

