Explain to me when I need to use an apostrophe ’ ? Example: nothin’
usually we write such words in songs
nothin’ = nothing
you’re welcome
i suppose americans allways write ’
It’s called an apostrophe.
The rules concerning the use of apostrophes in written English are very simple.
1. They are used to denote a missing letter or letters.
I can’t instead of I cannot
I don’t instead of I do not
it’s instead of it is
2. They are used to denote possession.
the dog’s bone
the company’s logo
Jones’s bakery (but Joneses’ bakery if owned by more than one Jones)
… note that we drop the apostrophe for the possessive form of it -
the bone is in its mouth
… However, if there are two or more dogs, companies or Joneses in our example, the apostrophe comes after the ‘s’ -
the dogs’ bones
the companies’ logos
Joneses’ bakeries
3. Apostrophes are 
NEVER ever used to denote plurals! Common examples of such abuse (all seen in real life!) are -
Banana’s 
for sale - which of course should read - Bananas 
for sale
Menu’s printed to order - which should read - Menus printed to order
MOT’s at this garage - which should read - MOTs at this garage
1000’s of bargains here! - which should read - 1000s of bargains here!
New CD’s just in! - which should read - New CDs just in!
Buy your Xmas tree’s here! - which should read- Buy your Xmas trees here!
Real life examples of apostrophe abuse! 
http://www.apostrophe.fsnet.co.uk/examples_1.htm
http://www.apostrophe.fsnet.co.uk/examples_3.htm
http://www.apostrophe.fsnet.co.uk/examples_2.htm
http://www.apostrophe.fsnet.co.uk/examples_4.htm
