first, whether you can get Family reunion depends on the Kind of Aufenthaltserlaubnis you have and when you got it.
Especially, if you have been granted only "subsidiären Schutz" (subsidiary protection) and after 16 March 2016 the right to Family reuinion is restricted. (In this case your relatives would not be allowed to apply for Family reunion until 16 March 2018). But if you have been granted normal refugee protection (normally this is the case if you have been granted permission to stay for 3 years not only 1 year) this restriction does not apply for you.
The procedure for Family reunion must be adressed to two authorities: the German embassy/consulate in Iraq and your Ausländerbehörde. The procedure is as follows:
Your Family (mother) has to apply for a visa for Family reunion at the German embassy/consulate in Iraq. Procedure of several months is normal for applying for a visa for Family reunion. The next step will be that your rmother should receive a date for an appointment at the German embassy/consulate in Iraq.
At the German embassy/consulate your mother will also be asked to provide documents of you (in copy).
Once your mother has received a visa from the German embassy/consulate in Iraq she must apply for a permission to stay at your Ausländerbehörde within the time-frame that the visa is valid for. (Besides: The Ausländerbehörde here in charge of you will be in contact with the embassy / consulate in Iraq but is not allowed to communicate with you directly regarding this matter.)
Pls feel free to ask if anything is unclear.