Curious about ' 's

I write a lot and I am sure most of you do which is why I am asking all of you if anybody knows an easy rule to remember wher to put an apostrophe.

The nurses office
the nurse's office

writers work
writer's work
writers' work

Can anybody please help me so i wont' have to use the grammar check everytime?? Even then I amn still confused because they give you 2 choices

So can anybody plesae help me out with this? How do you know? How do you remember? Is it different for plural or singular?

writers work -- as in multiple writers are working.
writer's work -- as in a singular writer's work.
writers' work -- as in multiple writers' work.

In shorts, an apostrophe signifies the possessive form of an object.

I don't know if this will help or not but its how I remember;
When you are saying 'the nurse's office' you put an apostrophe their because its hers *the nurses* but when you say this 'I have writers block' you don't put a apostrophe there because its not you block *does that make sense?*

And a Warning: This might not be right and it might not make any sense and it might ot help.

what if I mean nurses office as in plural nurse?
Would it be different from the singular one?

Indeed.

"Nurse's office" means ONE office owned by one nurse.

"Nurses' office" means ONE office owned by multiple nurses.

AH HA THANK YOU!

What if the original word ends in an 's'? That is the only version that confuses me. Like in this case:

The lass's dog.

In all forms: if there is one lass, more than one, etc. Is is lass', lass's, lasses, what?

*I couldn't think of any words that end in an 's,' but when I'm writing it comes up all the time. *Sigh*

Please help!