In English, showing ownership or possession can be done in several ways. In stiff, formal writing, one might read:
The car belonging to Mrs. Grant has now arrived.
However, most of the time we use the informal:
Mrs. Grant's car is here.
Usually, adding an apostrophe (') and then the letter "s" will accomplish this task.
Sometimes that doesn't work, however. If the owner already has an "s" at the end of his name, you only add a single apostrophe and nothing else:
James' car was blue.
When you pronounce James', you still say it "jaimzez".
I see this error quite often. There's a fruit stand north of North Ruralville and the large red-and-white sign reads, "JAME'S."
When you're making the possessive form of a plural word that ends in "s", you do the same thing.
We visited the Andersons' house last night.
Pronouncing "Andersons'" is the same as just saying "Andersons."