To make a diminutive noun you should add diminutive suffixes to the word stem. In Rus language we have some : ошк ,ушк ,чик ,чик,ышк,юшк and so on. There is no certain rule which suffix for which noun so when you want to make a diminutive noun you should check which suffix is used for this certain word. Until it become natural and you start "feeling"it, like native speakers do.

Good news: men use such words more rare than women.

There are very many specific cases for various categories of nouns. I don't think you need all these rules if you are not at an advanced level yet. I have a feeling that there are almost as many rules as there are nouns and adjectives. If you come across such nouns in your texts just remember individual cases for the time being. I would not advise you to try constructing diminuitive nouns yourself as the chance that it will sound wrong is very big. Moreover you have to take into account the subtelties of the situation when you can use them and when it will sound inappropirate. Sorry, it seems like that.

Hi! I think, you shoud take a noun and add the suffix. For exsample: mouse(мышь)+suffix(онк)= мышОНОК. This is called for Russian "уменьшительно-ласкательное существительное"

I've read the http://en.wikipedia.org/wiki/Diminutive page. And you know what? I have no idea what those diminutive nouns in russian. I suggest you to stop concentrate on the grammar and start listening to simple russian. If you want ever to master a language you should listen to simple language for thousands of hours.