Last parameter in INDIRECT if FALSE means we use within formula R1C1 notation.
Within address that's current row (0 as first parameter), 6th column (second parameter) using relative references (third parameter=4) using R1C1 notation (5th parameter=0) on sheet Summary last parameter.
Other words ADDRESS returns text "Summary!RC". INDIRECT converts it into real reference. Other words we take value from the cell in sheet Summary which is on the same row where the cell with formula and shifted on 6 columns to the right.
If we enter formula in A1 of our sheet, first INDIRECT returns value from Summary!G1. If formula in B3 - when value from Summary!H3, etc.