Plural is constructed with the letter S.
's (with apostrophe) is not plural. it's either:
Abbreviation of "is" - it is good / it's good
Abbreviation of "us" - let us go / let's go
Posession - The PC of Nicoll / Nicoll's PC
After all, you don't say flower's, forum's, phone's, laptop's, graphic's card's, letter's; rather flowers, forums, phones, laptops, graphics cards and letters. For some reason, a lot of people don't understand this...