All very good questions and rather than try to ask you a lot of additional questions so I can manually determine what memory your computer uses, I will simply tell you what I do when I need to buy memory.
I go to
Crucial.com where they have a System Scanner Tool that will scan your computer, determine what type and how much memory your system can use, and then offer to sell you just what you need. I have used Crucial ever since I first discovered them, many years ago and have never had any problems with their memory. They even give exact instructions on how to install your new memory.
If you don't want to buy memory over the Internet, then use the Crucial System Scanner Tool to find out what kind of memory you need, write the information down, and go to a local computer store to buy the actual memory.
Hope that helps.
[Added]
BTW, you need to check your Private Messages. I sent you a message. I have also moved your topic into a forum that is more appropriate for your question.