Welcome to Inkscape Community!
I guess the first thing -- do you understand the difference between vector and raster ("bitmap") images?
Inkscape is a vector editor. You will not be able to edit JPG or PNG images, at all (because those are raster formats).
It might be possible to edit PDF images, depending on how they are made. That's because PDF can contain both raster and vector images. So the only way to know, is to open them and look to see what's inside. Inkscape can open PDF files.
EPS is a vector format. (It might be like PDF, where they might have both raster and vector images, but I'm not sure) Inkscape can open EPS files, but it's not always easy, especially on Windows. The special instructions for opening EPS files on Windows are on the Inkscape website, which has unfortunately been offline for the last few days. Fortunately I happen to have a copy of the page its on. So the instructions are below. If you need help following them, let us know, and we can help
"Initially you need to find out where ps2pdf is on your machine or install it. It's in the Ghostscipt lib directory, which is probably something like C:\Program Files\gs\gs9.09\lib
If it is not installed you may find a current release of Ghostscript for Windows on their download page here. (
http://www.ghostscript.com/download/)
Then you need to add this to the system Path in Environment Variables. To navigate there on Win XP, Vista, 7: Start button > Settings > Control Panel > System > Advanced > Environment Variables. In Windows 8.1, right-click on This PC, choose Properties > Advanced system settings > Advanced tab > Environment Variables. Scroll through the System variables in the bottom panel, and select Path, click Edit. In the ridiculously small edit box provided add a semicolon to the end of whatever is there at the moment, and then add C:\Program Files\gs\gs9.09\lib (or whatever it is on your machine).
You will also need to add the Ghostscript bin directory to the system Path. (This will be the same as the lib directory, but ending in bin rather than lib - for example: C:\Program Files\gs\gs9.09\bin)
Note that updating to a new version of Ghostscript will install new \gs directory, but will not erase the old version subdirectory or update the Environment Variables. You'll need to do that yourself if you want to make use of it."
If you do manage to open and edit the EPS files, try saving as SVG. That will make them easier to edit again later, if you need to. If you'd like to use Inkscape to edit any new files that you download from the internet, try to find them as SVG files. Those will be much easier to edit, than EPS.
