Complex sentence: Once the left ring has a negative charge it attracts positive charge to the left spout, so positively charged drops fall from the spout to the positively charged bucket, making that bucket even more positively charged.
Split into simpler sentences: Once the left ring has a negative charge, it attracts positive charge into the left-hand stream. When drops break off that stream, they carry positive charge to the positively charged bucket, making that bucket even more positively charged.