how to use xsd namespace

I have searched many places for namespaces, but doesnot get satisfactory answer

for the following xsd file

<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"           targetNamespace="http://www.example.org/schema"           xmlns="http://www.w3.org/2001/XMLSchema"           elementFormDefault="qualified"><xs:element name="product"/></xs:schema>

for the above code, following are my understandings. please correct me if i am wrong. Also i have some query regarding the same:

1. xmlns:xs="http://www.w3.org/2001/XMLSchema" is the place where defination is stored of all the elements and datatypes i am using in my current document.

2. targetNamespace="http://www.example.org/schema is actually the package name where the current file is going to be stored.

3. xmlns="http://www.w3.org/2001/XMLSchema" : no idea what is this

4. **xmlns:tns** is same as targetNamespace. then why we use it seperately?

5. what is use of first and third line