All you need to do is specify the fields, here I take the default of * and the feature class. You can reduce the number of rows by passing a query as well.
Code Sample Run From Python Window:
with da.UpdateCursor(r'C:\temp\scratch.gdb\floodsub', "*") as urows:
... for row in urows:
This little sample just erases the first row in the feature class. The 'with' statement automatically closes the cursor object, so it does not have to be manually deleted. This ensures the locks are removed on success or on failure.