MySQL Newbie have a problem (easy question, please help)?

[mySQL Newbie]

OK, i'm now at Chapter 8 on some book about database, mySQL .

Now i have this problem, i understand the concept about composite key and foreign key.

The syntax for primary key is like this:
CREATE TABLE [table_name] ([column_name] INT NOT NULL AUTO_INCREMENT PRIMARY KEY);

Could you guys write me the syntax to create a foreign key and a composite key. The composite key is the most important.

Oh, and one last easy question,

What does this text do in mySQL :

CONSTRAINT my_contacts_contact_id_fk.

I know that CONSTRAINT is like a thing that gives an error if you give the foreign key a value that didn't exist on the primary key. Could you guys explain it more thorough. Please help me.