[GAP Forum] help

[Takjk Taj]

Dear GAP forum,
I would be grateful if anybody help me about the following questions.  

1) For a normal subgroup $N$ and a subgroup H of $G$, how we can compute the product
$HN={hn|h\in H and n\in N}$?
2)For any $R$-module  $M$ and $N$, how we can compute the tensor product $M$ and $N$?
especially when $N=\mathbb{Z}$.
3) Let two groups $H$ and $K$ be given. Can we obtain the central product of $H$ and
 $K$?
Any suggestions are welcome.
Yours,
Takjk