Some people from other schools of thought say that tawassul and istighatha are the same as shirk. Can you explain to me if it is/isn't and why it is/isn't?

n brief, Tawassul and Isteghatha are not shirk because:

1- The one who does them is not worshipping the Prophet/Imam. He only worships Allah.

2- Allah has commanded us to seek their intercession. Just as Allah commanded the angels to prostrate to Adam. Was that shirk?

For an in-depth discussion on this, please see:

You may see the last one especially.