If you go back even farther, you can probably find other message threads that also deal with aspects of this subject. This might be a good time to experiment with the forum's Search utility.
The "Save Timeline Snapshot to File" button on the Video Preview window toolbar will do that, and place the file in the Media Pool window, where it can be placed on the timeline. Be sure to right-click in the Preview and turn ON "Display at project size". Set the Preview quality to "Best". You might also want to set your project property "field order" to "None (progressive scan)" and the advanced property "Deinterlace method" to "Interpolate fields" to get the back still image quality. Set the field order back when you're done making snapshots, or your final render won't be right.
-OR-
Use video event velocity envelopes to slow down and/or stop the motion in a clip, and restore it when you're done holding the still frame. Read about "velocity envelopes" in the Help or Manual.
SonicDennis gave you a good recipe for doing the deed. To give you some more perspective on this, the following are some recent related threads gleaned from the Search utility: