My Little Grammar Guide

Those three are generally correct, but there are fiddly bits.

Don't use one for possession when using pronouns.  Hers, His, Its, Yours. There are probably more.

It's means It Is.  Its means the It in question possesses something.

There's some discussion on this one, but as a rule, when using one for possession, and there's an S at the end of the word, it goes after.  My grandparents' place.

The debate, for the record, is whether doubling up is acceptable. IE: grandparents's.  Generally not accepted, but it is a discussion.

It's accepted practice, and I highly recommend it, to begin a word that has been shortened on the starting end with an apostrophe.  For example: Because becomes 'Cause or Until becomes 'til.

Incidentally, using till when people mean 'til is a pet peeve of mine.  Till is the word meaning to turn earth for planting.  'Til is the short form of until.