Proposition of complexes in Homology

Question

I have been reading Maclane's book on Homology and he talks about the following proposition :

"When the ring $R$ is regarded as a trivial complex then $Hom(R,L) \cong L$, under the natural homomorphism wich assigns to each $f_p: R \rightarrow L_p$ its image $f_p(1) \in L_p$."

I have two questions that are,

1) What does he mean by a trivial complex ?

2)This isomorphism is in the context of the category?

Thanks in advance.

Answer 1

(1) The trivial complex is the complex that has $R$ in degree $0$ and has $0$ in all other degrees. (2) It's an isomorphism of complexes of $R$-modules.