How to show that the set of all $n \times m$ matrices over $R$ forms an $R$-$R$ bimodule under addition?

How to show that the set of all $n \times m$ matrices over $R$ forms an
$R$-$R$ bimodule under addition?

How to show that the set of all $n \times m$ matrices over $R$ forms an
$R$-$R$ bimodule under addition? (when $R$ is a ring and the $n \times m$
zero matrix as the additive identity)
Actually what I know, if every ring $R$ has associative multiplication and
hence is an $R$-$R$ bimodule. Every left module $A$ over a commutative
ring $R$ is an $R$-$R$ bimodule with $ra=ar$ $(a\in A, r\in R)$.