tawassul

Q: What is the difference between Istighathah, Waseela and Tawassul? I have read that Waseela and Tawassul are permissible whereas Istighathah is not permissible and could lead to kufr and shirk.

Q: On this website muftionline.co.za I was browsing and in one question a person asked if we can supplicate through an intermediary i.e through tawasul of a righteous one, living or dead e.g through Sheikh Abdul Qadir Jeelani...in which the answer was gives yes..I was suprised to see this answer. How could this be possible if it is written dead or even alive. This is a clear form of major shirk. We ask Allah directly. There is no dipute among any knowledgebale scholar or pious predessor in my understanding regarding this. I am 100% sure. How can this be possible. How can a dead person or alive person benefit us when Allah states in the Quraan clearly to ask from Him. Even asking through the Nabi Muhammad (Sallallahu Alaihi Wasallam) is not allowed. Can you please explain?