Grid representation as a graph

I am thinking of a grid and suppose in the grid '#' represents that the way is blocked and '.'(dot without quotes) represents there is a way.So if A is inside the grid then he can walk inside when he found way(.) e.g.,

#######
##A####
##.#.##
##.#.##
##...##
#######

for the above example, A found the way and he reaches to other place like this below in picture:

#######
##.####
##.#A##
##.#.##
##...##
#######

If I am thinking this problem as a graph then How I will represent this grid as a graph ? How to represent this as an adjacency list ? I am new to graph just stuided BFS only, please answer in easy words