## but there was a certain man ##
"a certain man…names Simon" is a way of introducing a new person into the story. You need to be aware of how new people are introduced in your language. (See: en:ta:workbench:discourse:home)
## the city ##
"the city in Samaria."
## all the Samaritans ##
This is a hyperbole for "many of the Samaritans in the city." (See [[rc://en/ta/man/translate/figs-hyperbole]])
## This man is that power of God which is called Great ##
People were saying that Simon is the divine power known as The Great Power.