Transforming (conjugating) verbs


So I am studying from an online site called Memrise but they seem to teach
pretty straightforward stuff that you have to memorize in order to do them.
Yeah I can ask and say things but I can notice that the verbs change when the
context changes. Some examples:

The verb is usually

> **はたらきます** ( _to work_ )

but in this context

> かれはオフィスで **はたらいています** 。( _He works in an office_ )

it transformed to a brand new version of the verb. Now I have memorized them
both but if I wanted to say something else I'm drawing blanks.

And here's another example. I noticed a pattern between these next few but I'm
still not sure how they transform:

> どうしてそんなに **かなしんでいるの** ですか？(Why are you so sad?)

correct me if I bolded too much. I'm not sure if the の particle is included in
the verb here. The verb is usually **かなしんでいます** but here it transformed to the
bolded part. This one totally confuses me. It's different from the next one
because in addition to having the verb have いる at the end it also has the の
particle. I know it's a possession particle but its use here is beyond me.

And here's the third example where it's really similar to what we saw in the
second example:

> わたしは **おなかがすいている** から、おこっています。( _I'm hungry therefore I'm angry_ )

Right here I can tell that the verb is the bolded part and the から particle is
used to show a reason meaning _therefore_ in this context.

Do these transformations have a name? Something I can research online or from
some text book. I see that the verbs have these forms but I can't group them
in one category so I can research them. They seem quite random.

There are many others that baffle me like "ふん" -> "ぷん" in some sentences. But
I guess that's it for now. I really want to go a bit deeper in the grammar so
I can improvise in my free time by creating sentences in my mind and not mess
them completely up.




This is usually known as verb conjugation. Japanese verbs have a stem, and are
then conjugated to change their meaning. In your first example, the stem is
「働{はたら}」, meaning to work. The second part is the conjugation, 「きます」, which is
added on to the end of the verb stem to transform it into the "present
indicative polite" form. You can see some of the conjugations of 「働{はたら}」
[here](http://japaneseverbconjugator.com/VerbDetails.asp?JapaneseVerb=hataraku&VerbClass=1&EnglishVerb=work).

