ConwayLife.com

Hello,
For example the initial matris is A.
A= [a b c
d e f
g h j]

What are a's neighbours? (0 live,1 dead cell)

"b d e" or "0 0 0 0 b 0 d e" or "1 1 1 1 b 1 d e"

What will we choose a's neighbours?

I assume you're talking about a bounded grid? If so, the neighborhood for cells on the edge depends on the topology you want (plane, torus, sphere, etc). The various topologies supported by Golly are illustrated here:
http://golly.sourceforge.net/Help/bounded.html