Sort results by number of using

[eluser]someone [/eluser]
Hello!

I would like to create model's function which will shows most used categories. I have two tables - news and categories.

Table news: ID_article, title, content, date, ID_category, url
Table categories: ID_category, title, description, url

So this function must get number of using for each inserted category and this must be limited with 5.

Like this output:
Number of using | Name | Description
23 First First category
21 Second Second category
8 Third Third category

Thanks for help!