In case you haven't realized it yet, noma 々, or kurikaeshi 々, or dounojiten 々, or some other Japanese name for this damn thing, is the elusive repetition kanji. I repeat: it's the repetition kanji. Why is it called the repetition kanji? Because it repeats the kanji, that's why.
When you have a word that has the same kanji twice (repeated) like hitobito 人人, you might feel like it's a pain in the ass to write and a pain in the sight to read the same kanji two times in a row. So, instead, what the Japan did was make a kanji that you can use to mean you are repeating the last kanji. Like this: hitobito 人々.
So every time you have the repetition kanji 々 in a word, you are just repeating the last kanji. It's its substitute. It's a shortcut. An abbreviation. The writer means 人人 but writes 人々, so when you read 人々 just pretend it's actually written 人人 and that will save you a lot of trouble.
Words With 々
Of course there are more words with the repetition kanji 々 in Japanese. That's why it's worth explaining about. Here are some examples:
- hitobito 人々
- hibi 日々
- samazama 様々
Various (things, na-adjective).
- iroiro 色々
Various things. Stuff. (substantive).
- nakanaka 中々
- tamatama 偶々
Accidentally. By chance.
- dandan 段々
- masumasu 益々
- tsugitsugi 次々
One by one. One after other.
- tokidoki 時々
- souzoushii 騒々しい
As we can see, both the reading and meaning of the repetition kanji 々 varies according to the word. After its function is to vary depending on the kanji preceding it. That's why 々 has so many different names, because it actually means nothing and has no reading of its own.
This is obvious, but let me state it anyway: there are no words in Japanese that start with 々. After all it needs to go after something to have meaning at all.
The 々 kanji doesn't just repeat the sound or reading of the previous kanji either. For example, in the word dandan 段々 (段段) we have two simple dan's. It's the same sound twice. But in samazama 様々 (様様) it's one sama and one zama. This is because sometimes a kanji reading is voiced, sometimes it is not, the 々 just repeats the kanji, so if it's supposed to be voice it should be voiced. The reading of 々 won't necessarily be identical to the previous kanji.
Why Are There So Many Words With Repeated Kanji?
Now maybe one very important question that everyone will end up asking one day is: why are there so many words with repeated kanji, repeated syllable patterns like that? Just... why?
Geez, I don't know. It's just the way the language is. Try not to worry about it. Personally I think words like that are funny.