Using japanese numbers

[whitemann]

Konnichi wa!

Can someone please explain me, when to use:
hitotsu
futatsu
mittsu...
... and when:
ichi
ni
san...

I have noticed in the japanese animes that they commonly use <ichi/ni/san> and I'm not sure when to use both of these number sets, if I can call them that way...

 

[Toritoribe]

In Japanese, virtually all nouns must use a counter to express number. In this sense, virtually all Japanese nouns are mass nouns. This grammatical feature can result in situations where one is unable to express the number of a particular object in a syntactically correct way because one does not know, or cannot remember, the appropriate counting word. With quantities from one to ten, this problem can often be sidestepped by using the traditional numbers (see below), which can quantify many nouns without help. For example, "four apples" is ringo yonko (窶堙ｨ窶堙ｱ窶堋ｲﾅｽlﾅ津? where ko (ﾅ津? is the counter), but can also be expressed, using the traditional numeral four, as ringo yottsu (窶堙ｨ窶堙ｱ窶堋ｲﾅｽl窶堙?. These traditional numerals cannot be used to count all nouns, however; some, including nouns for people and animals, require a proper counter.

Japanese counter word - Wikipedia