-Ing meaning

I. Till now, I just know V_ing is used in some tenes and after preposition so when I see these sentences below, I'm confused. So please explain to me:
1) He got back to the shool yard, trying to find his ball once again.
2) Tom, a six-year-old boy living in our neighborhood is very fond of games.
3) He was given a task of getting information on the Thi Nghe ammution depot.
4) They’re going to build a building rising up into the sky.
5) I actually find walking is very relaxing
Sometimes people use V_ing at the beginning of sentence Ex:(I dont remember exactly) Walking on the street, he looked for her.

II. Please show to me the different of these 3 words:
gotta,gonna,wanna
I dont know when to use them and why people use them.

III.THANK YOU VERY MUCH!GOOD LUCK!
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The -ing form of a verb is the present participle. The most basic form is in any progressive tense (I am running, She was writing, etc.). It can also act like a noun (I like reading, Sneezing is stupid, etc.). The first two sentences and the fourth one only seem confusing b/c they leave out redundant information (He got back to the school yard, and was trying to find his ball once again; Tom, a six year old boy who is living in our neighbourhood, is very fond of games). The third sentence is tough to describe, I guess it's acting like a noun. The fifth one it is definitely acting as a noun. (The way an English speaker would say this is "I actually find walking very relaxing).

Also, gotta is contracted "got to" meaning "I have to" or "I must." Gonna is contracted "Going to" not in the sense of direction, but rather as a future indicator (I'm gonna go home). Wanna is contracted "want to."

Please don't use "gotta, gonna, wanna" when you talk to Brits. These words can sound substandard over here.

Unfortunately you have to use them when you talk to Americans... Otherwise it sounds unnatural.

"-ing" can denote the progressive mood of a verb (I am walking), a present participle (The walking boy) or a gerund (I hate walking).

1. Present participle (verb as adjective), modifying "he"

2. Present participle, modifying "boy"

3. Gerund (verb as noun), object of preposition "of"

4. Present participle, modifying "building"

5. Gerund, object of verb "find"

Gotta = got to (or have got to)

Gonna = going to

Wanna = want to

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If you don't believe me, please ask mansoor47k@yahoo.com. He was sent my gift in the last topic and I tell the truth!
Anyway, Thank you very much again!GOOD LUCK!