Well, first of all know that this may take awhile...some people take months to "finish" grieving, others take years. Also know that there is no "real" way to grieve...manly or otherwise. In other words, crying is ok. It's also ok to feel upset, angry or guilty...you've lost someone you loved.
Some things you can do is to talk about your grandfather with people who you're close to, who also knew him. Talking about things you liked about him, and things you maybe didn't quite like. Visit places that remind you of him, and remember the things that happened there.
It's important to not block out or repress these feelings and thoughts. Doing so is going to negatively affect your mental health in the coming months and years. If you ever feel like talking to someone, and can't find someone, you can always call a crisis line (http://www.depression-understood.org/information/ukcrisisline.htm) they're open 24 hours and, assuming that they are like the crisis lines here, they will have received training to deal with grief (as well as other crises you may experience in the near future...depression, suicide, etc).
