If you're using Chrome, there could be a problem if the videos you want to capture are on Youtube. You're not meant to save Youtube videos to your hard drive because it infringes copyright legislation and break's Youtube's rules (but don't worry though; everyone does it!). Since Youtube is owned by Google it's unsurprising that Google won't allow any Youtube downloading add-ons to appear on the Chrome Web Store (because they're also behind Chrome). If you want to save videos that
aren't on Youtube, you could try this:
https://chrome.google.com/webstore/detail/fvd-video-downloader/lfmhcpmkbdkbgbmkjoiopeeegenkdikp?hl=en
(I've no experience of it; it just seems to be well-reviewed).
If you want to save Youtube (or, indeed any other) videos, I recommend downloading and installing Firefox:
http://www.mozilla.org/en-US/firefox/all/
(You can have as many different browsers as you like on your computer. You could either choose to switch to Firefox for all your web browsing or just use it for saving videos). Then install the Ant Video Downloader, using my link above. Once you've done that you'll find that there's an extra button at the top right of your Firefox screen, with a little downward arrowhead next to it. Click the arrowhead and select 'Preferences'. You can then choose the location you want to use for 'Downloaded Movies Folder'. Once you've done that, simply go to a page containing a video you want to save and click on the 'extra button'. The video will automatically be saved to where you want it.