You are confusing the binary operations in the two sets A and End(A). The definition of + in End(A) is: , (f+g):A→A where (f+g)(a) = f(a)g(a) for all a ∊ A.
This may look strange, but that’s because you are writing product of elements in A multiplicatively.
However, since A is an Abelian group, why not denote the binary operation in A additively? To avoid confusion, let’s write for the operation in End(A) and + for the operation in A. So we have
for all a ∊ A.
Now that looks more intuitive. Hence, for any endomorphisms f and g and any :