Type the same Normal-mode keys on every line of a range.
3 drills
Every line at once: Make the same change on every line with one :%normal command (:%norm for short).
Only the selected lines: Change only the paragraph the cursor is in: select it with vip, press : (the '<,'> range appears) and finish with normal and the keys.
Motions and operators too: Any Normal-mode command works, not just inserts. Apply the change to every line with :%norm and an operator plus a motion or text object.