See the first bullet point, the link “MDBG Bookmarklet” ? Right click on it, select “Bookmark this link”. You now have a bookmark called “MDBG Bookmarklet”. Select/highlight a single kanji character in the text of a web page – for instance from the left column on this page. Now select “MDBG Bookmarklet” from your bookmark menu.

Be careful not to click elsewhere on the page when selecting the “MDBG Bookmarklet” as that might deselect the kanji in the page text.

Actually, you can select multiple kanji characters and MDBG will return the meanings for each.

Hey, man. 🙂 I’ll see if I can help you out with bookmarklets. They confused me for a while, too. Everywhere I’d look, people were talking about these great bookmarklets but nobody ever said how to actually USE them! Haha. So, here we go.
Basically, you make a new bookmark in your web browser of choice (hint: the cool kids use Chrome ;P). You set the name of the bookmark to whatever you like, and instead of putting a URL like you would normally have, you place the Javascript code for the bookmarklet (so, for this bookmarklet, everything from “javascript” to that last “()”). Then to use the bookmarklet, simply click on it in your bookmark list. For this bookmarklet specifically, you highlight a kanji on a web page, then click the bookmarklet. The bookmarklet will then open a new tab featuring a page of a website with the information for the kanji you highlighted. Other bookmarklets work in a similar way. Just play around with them and see; it’s what I had to do, and it showed me some cool stuff. 🙂

Hope that helped! And please, anybody, correct me if I got some information wrong.