How do I access my Mobile Facebook app?

[Net]

I downloaded the app for Facebook and is a great app great to work with. However, it doesn't give me an icon for the desktop or an icon in my applications. it's not listed under my downloads either. nor in my bookmarks. when I was in it it did not allow for me to make a bookmark for it. I cannot for the life of me figure out how to get back into this app. when I attempted to reinstall I couldn't find the original app that I installed online. if you need to know my phone, it is an lg optimus m plus. important point..... I do not know what "root" or any of those terms mean. I am a beginner with any of this technology on mobile phones.