Here’s what that snippet of code does:
M221 S100 T0
This sets the “flow rate” for the printer to 100% flow (the normal flow rate) at extruder “0” (T0). A dual-extruder printer would have T0 and T1 … your printer only has a T0.
This resets the E axis (the extruder) to the “0” point. This is does so that any extrusion performed in absolute mode will be relative to that position.
G1 F600 E-1.75
This causes the printer to pull back 1.75mm of filament (it is a retraction move) at a Feedrate of 600mm per minute (10mm per second).
The next few lines are comments (anything after a semi-colon is a comment)
G0 F10500 X66.678 Y126.706
This performs a move to that X/Y coordinate position (leaving the Z height alone) at 10500mm per minute (which works out to 175mm/sec). That’s a fairly fast move and presumably a non-printing move.
But then you get two more fast non-printing moves (these are very short distances). The 3 sequential moves are basically controlling the path that the printer takes. You could just go straight to the 3rd move position and ignore the intermediary moves … but it may be doing this to move around something or follow a specific path (e.g. if “wiping” or “combing” is enabled.)