Can you help me write some .htaccess for switching how something is called?

I tried to describe it as best I could in English in the title, but here is what I am looking for some code to do. I hope you can help me:

The script currently calls like this: root.com/?b=this+plus+sign+separates&g=1

the &g=1 doesn't always get called, and if it is called, only occurs in that fashion, so there is no &g=2, etc

I would like .htaccess that would rewrite the URLs so they could be called like this also:

root.com/this+plus+sign+separates/g/

I'd like g/ to be added for functionality, so like &g=1, it is not added to every URL, but if someone were to type it, it would be a replacement for &g=1.

I'd like the trailing slash to be appended, but it to work without it.

For example, here is a tutorial I found for another project about how to rewrite extensions to use directory form:

http://eisabainyo.net/weblog/2007/08/19/removing-file-extension-via-htaccess/

I want it to work like the code with trailing slash, where it can be called either way.

Please, let me know if I have been unclear in any way, or if you can help me with a solution.

Thank you.