after dedication ritual ,how do I talk to father satan ??Do I need to meditate on his sigil just by looking at it or I need to visualise the sigil in my mind?
Either or works. If visualizing is too distracting and not something you're used to then just getting into a meditative state while looking at His sigil works just fine.
Getting better at visualizing is something that you would want to do as well but for this specific part, whichever is more comfortable for you is fine.