XML : PHP/XML feed reader where to start?

I have a question regarding XML feeds.

There is a website whitch provides data and they give me 2 links for 2 files

• file 1 : Cars_docu.atom
• file 2 : Cars.atom

date on file 1 is like this

   <entry>  <author>    <name />  </author>  <f:name>Name</f:name>  <f:description>Product name</f:description>    

and the second file is like this

   <entry>  <title>Volvo</title>  <link rel="alternate" href="#1" />  <author>    <name />  </author>  <id>237370</id>  <updated>2015-08-17T11:44:32Z</updated>  <f:name>Volvo Lamp</f:name>    

So as I understand the first file includes name of the filds and the second one includes the data

My question is what is the method of pulling this imformation from both files using a PHP file and gather them into one page ?

and inside the second document there is a 10000 product so how i pull one pacific product only?

I need methods if you have code I will be glad or just tell me where to start

regads