Most of the CAD systems provide a command to save as an image the current view. Usually, this command is available in the "save as" menu or in the option menu
The following picture shows the "save as image" command in Solid Edge (Solidworks has a similar command)
CATIA provide a capture command in the tools menu
In case your system does not provide a "save as image" or a capture command, then you can use the "print screen" function available on the keyboard of your PC: look at the keyboard and find the PRTSC key (usually it is a function key, that means that you have to press the FN key and the PRTSC keys simultaneously). This action will copy the image of your screen in the clipboard; then you can use any image editor (like windows paint) to copy and save the image.
You can also use the windows capture tool to capture the whole screen or just a region