I have a granite m/p from the place I link to below, which has helpful usage instructions along with recipes:
I roughly followed these guidelines to season mine; it's probably more than necessary, but it also lets you get familiar with the m/p before you use it for real cooking:
Have fun with it!
I have a granite mortar and pestle. I did use soap to clean the first time, but I understand that people are concern about cleaning it with soap/detergent regularly due to flavor residue. Some mortar and pestle require more seasoning than others. For example, Molcajete requires extensive seasoning, while glass mortar does not. Usually, for a granite mortar and pestle, grinding white rice should be sufficient.
I am not an expert in mortar and pestle, so I am offering my amateur understanding. Best of luck.