You can not open scut files unless you have scal open and do it from the File drop down at the top in scal.
If you don't have inkscape you can not open .svg files unless you have the scal program open and use the SVG button at the top.
I can not think why else there would be a problem. When you download a file from the internet you just save it to a folder on your computer or to the desktop initially so you can find it easily.
Is your cricut firmware up to date? On craftedge homepage, please read all the info to get started, plus tutorial section.
Should you continue to have problems you can email
support@craftedge.com and they will get back to you quite quickly. Give them as much information as you can think of relating to your computer and what is happening.