Hi T,
Ok.... with the image on the screen AND as large as possible, for maximum resolution,
1. PRESS the PRT Sc (Print Screen) button, usually situated above the home/end/page up/page down/Delete/Insert block of keys on a standard keyboard. This copies the image into a buffer for use in another program.
2. Open the program in which you'd like to use your image: Microsoft Paint, Word, Power point etc.... and select "Paste" or Sometimes "Special Paste" or good old "Control V" to insert the image in to the document, file etc....
It is well to remember that the image is a copy of whatever was on the screen at the time, so make sure the image is as large as possible on the screen and that the screen is set to the maximum supported resolution in the Windows screen settings. Microsoft Paint is a useful initial cropping tool for your image and will work to produce an image of various required formats, in case your application doesn't accept it directly as a paste from "Print Screen".
BUT for Adobe Premiere Pro (Video editing) there should be a direct image /frame grab tool that outputs the video frame as typically a JPEG to a file. I know this is the case for Pinnacle Studio and I imagine the same for Adobe. In any event, the process above will always work, which can be useful on trial software which often (sometimes ?) will not allow any printed output or saving of files.
EDIT: Added You tube Link to Adobe Premiere Pro Frame Grab / Export:
Have fun,
Best
JA