What dose -er mean when added to a word

When the suffix -er is added to a word it means a person who

-er can mean one of two things.
If it is added to the end of a verb, it means a person who performs this task/action (ex. runner, swimmer).
 
However, if it is added to an adjective (or sometimes adverb) it is the comparative version of that word and it is comparing two things as saying one thing is better at doing something, or more than the other thing (ex. lazier, hungrier).

This is what i found on google “eightin 1997, the mccaughey septuplets were born in carlisle, iowa. multiple births of as many as eight babies have been born alive, the first set on record to the chukwu family in texas in 1998; one died and seven survived. in 2009, a second set, the suleman octuplets, were born in bellflower, california.” i was surprised about this . i don’t want to have that many babies .