2.  er was added to roll to turn it into roller. Roll is the root word.  Look what happens to the meaning of words when er is added:

roller = something that rolls
teacher= someone who teachers
painter= someone who paints
fire fighter= someone who fights fires

3.  Listen to the ow sound in allowed.  Is it the same sound you hear in cow or in snow?

4.  If a word ends with an ed or er, you can cover up the ed or er to get to the root word or main word.  This can help you figure out a new word.

1.  Make a list of words that end in er.

2.  Make a list of words that end in ed.