plugin internationalizing problem

Dear Users,

I’m programming a new plugin and I want to make it support more than one language & as the docs saying that first I have to write the expressions like this
__() or _e()
and then I have to use the xgettext tool ! my problem is here ! I don’t know how to use this tool ! I already installed it but it doesn’t work ! as they are saying this tool creates a PO file which contains all the expressions which wrote in this way __() or _e()
so is there any alternative program ?

Waiting your assistant.

Regards,
Feras Allaou