over the last few days i have felt the god of war reaching out to me but i am still unsure whether it is his greek or roman essence. how can i know which one it is and in what ways can i serve him?
First you figure out if it is Ares or Mars, because they are really quite different. That involves striving to understand the call you are feeling as well as understanding the myths and cultures of both figures.
And if all you feel is "god of war," it might not be either of the two.
Religious enlightenment does not generally develop over a few days. See if you still feel the same in a week or a month or a year.
There is a huge list of war type gods out there so if they did exist it could be any one of over 100. To tell which one would probably be closer to your heritage. Though they tend to vary. The best way to serve a god of war would be to die in battle.