Using Kanji

Im not entirely sure, as im very very much a beginner with Kanji, but i have noticed that Kanji is used for many, probably all(?) Nouns and Pronouns, in other ways too, such as 私 (watashi=I) like i said though im not entirely sure^^; although i do believe that that is correct, i may be wrong but hope i helped in some way :[ lol

 Well, for me, Kanji is used widely on almost every parts of Japanese language. Well when some words are similar to how they are read and written, you use Kanji to differentiate them. just like this :
せんたく are :
選択 - selection
洗濯 - laundry
they both are read the same. another example is 厚い and 暑い (あつい) which sequentially mean "thick"(as in "a thick book") and "hot"(as in "the weather's hot")

Another use of Kanji is, in my opinion, to make sentences look short so it could fit more on paper. just like in this sentence :
わたしはにほんごのうりょくしけんをうけます。
and
私は日本語能力試験を受けます。
which means : I attend the Japanese Language Proficiency Test.

so Kanji is used to state a specific meaning, and to shorten sentences. But not every word of Japanese language has Kanji form. CMIIW ^_^