Windows 7 is a rich environment with many components and tools. You add a lot to your computer over time as you create documents, copy pictures, create spreadsheets, store music, etc.
Finding what you are looking for can be frustrating.
First, when you create or copy something, make certain you name it such that you will be able to recognize it from its title. Second, make sure you store it someplace logical, and know where that is.
When you are trying to find it, you can use the universal search tool built in to Windows 7. Simply click once on the start globe on the bottom left and up comes a box into which you can type text. Type in a name that describes what you are looking for. A list will pop up above that box almost instantaneously. Click on any thing in that list and it will open the file you are looking for.
You can also find Windows elements there. Things like the snipping tool, defragmenter, and programs that you want to start.