There's something I don't get about attack i want to get straight : who decides who is committing first

For example, let's assume this position : https://i.imgur.com/RcrnJro.png

My move is attacking burma, his move is attacking india. What are the conditions for him to succede?

The order in which orders get executed is as follows:

A
B
B
A
A
B
B
A
etc...

Then, on next turn, players A and B are switched, so player B moves first and A moves twice and etc.

Who is Player A on the first turn, however, is random.