I have just recently started using blender and I am following a few tutorials to get a good idea of how to use the software. I saved a JPG file by selecting it and clicking save as but when I try to add the image as a texture it does not appear in any of my folders and I cannot access it, I tried changing what the files filter out but even when I have all files visible to select, I cannot find any of the images I saved in the folders I place them in. I have blender on Windows 10 and have the latest version as of July, 26 , 2016.
Two things - from your post it sounds like you were saving a texture from the web to use as your texture on your graphics. There is a possibility that the texture was BLOCKED from saving; some sites do that. If you have the ability to try again I would go back to the site. Make a new folder "my practice folder" and save the graphics to that folder. If they still don't show up AND you can see other graphics saved to that same folder (as a test) then you will know what the problem is.
A very handy way to see what is in the folder visually is to look at the files as graphics.
Secondly when you get ready to use a graphic as the texture for your model, you need to ASSIGN a MATERIAL to the parts of your mode that texture will go on AND you need to MAP your model so that it can accept the texture.
There are plenty of tutorials explaining this in detail if you need them.
You don't specify what platform you are using (Win, MACos, Linux, or something else), but you can find the file using a OS level search. In the file system search engine use the name of file, and if you did not happen to have chosen a unique name for your image file, the date you created the file, and the OS search facility should provide you the path to which you saved it. With that information, it should be easy to find the file, and perhaps move it to a more desirable location.
A little preventative effort goes far here. Before you start a project, create a home for it, and store all related elements in that folder as you make them.