[,] means each second array [x,this] are the same size but [][] the second arrays [x][this] can be different sizes. ie [,] is a 2d array, but [][] is an array of arrays, a 1d array of type array
So if you want (for example) a map then [,]
If on the other hand you want a map with what units are in each square [,][]
In your example Array:Int [5,5] is a 5 by 5 array of type Int
While Array:Int[][] = [New Int[5],New Int[5],New Int[5],New Int[5],New Int[5]]
Is a 5 segment array of type 5 segmant int array
So if you want (for example) a map then [,]
If on the other hand you want a map with what units are in each square [,][]
In your example Array:Int [5,5] is a 5 by 5 array of type Int
While Array:Int[][] = [New Int[5],New Int[5],New Int[5],New Int[5],New Int[5]]
Is a 5 segment array of type 5 segmant int array