Please correct any mistakes.

(Saying you're wrong suggests you're making an argument)

Yesterday I went to my friend's wedding party.

(don't forget the possessive form 's)

It was so fun. Many of my old friends came to the party.

(Use 'many of' before a pronoun or noun with a determiner 'my' and 'come' conjugates to 'came' here)

It took 30 minute to get to the place by train.

(You need not restate that is was held there as 'the place' can be used as an anaphoric reference.)

The building at the venue is very huge and clear. I was astonished.

('so' isn't usually used as an adjective in this way only when reporting on something true as stated or in informal contexts. Also try adding a prepositional phrase such as 'at the venue' )

The party was finished (after/in) 2 hours. I had a good time.

(You may use after or in.)

Besides (that), I met the man who taught social studies when I was at junior high school.

('Beside' is not used as an adverb. I'm sure you can use 'then' also but that would mean the following would refer to more recent events. No need for 'was'. Society could be replaced with social studies, but it is okay since the meaning is still clear. 'at junior high school' or 'a junior at high school' the latter implies you were in fact a junior the former alludes that you simply attended.)

He brought old memories back. I talked a lot to him (about many old stories/and we reminisced.)

('to bring memories back' so 'brought'. No need for 's' in 'a lots'. 'talk' is usually collocated with 'about' so 'talked about any old story' however 'any' suggests a sense of indifference. Perhaps you could use 'many old stories' ? You could also say you both reminisced.

Hope this helps,

Raharuhi

Daily

Yesterday i went to my friend's wedding party.
It was so much fun. Many of my old friends came to the party.
It took 30 minutes by train to get to the place that it was held.
The building was so huge and clear. (I'm not sure what you mean by clear - empty?) I was astonished.
The party was finished in 2 hours. I had a good time.
Besides that i saw the man who taught Society when i was in junior high school.
It brought back memories. I talked a lot to him, remembering some old stories.

(It's not clear whether you saw the man at the party - I've interpreted it as something else  that happened yesterday)

Daily

Yesterday i went to my friend's wedding party.
It was so much fun. There were many my old friends comes to party.  Many of my old friends were also at the party. 
It took 30 minute to get to place by train that where it was held.
The building is so huge and clear. I was astonished.
The party was finished in 2 hours.( The party was 2 hours.)  I had a good time.
Beside then that i met the man who was taught Society when i was in junior high school.
memory back. I talked a lots to him any old story. We talked lots about all the old stories.

(Anything that has been highlighted has been added or changed. Anything crossed out has been completely rewritten.)

Daily

Yesterday I went to my friend's wedding party.
It was such a <strike>so</strike> fun wedding. There were many people at the party, many of whom are my old friends. <strike>comes to party.</strike>
It took me 30 minutes to get to the place <strike>by train</strike>  where the wedding/it was held by train
The building is so huge and clean. I was surprised /  astonished > this is a "stronger" word
The party was over<strike> </strike><strike>finished in</strike> after 2 hours. I had a good time.
Besides that,  <strike>then</strike> I met <strike>the</strike> a former teacher who used to teach sociology at the  junior high school where I was a student years before at the wedding. <strike>was taught Society when i was junior high school.</strike>
The meeting brought back a lot of old memories. <strike>memory back.</strike> <font color="#0000ff">I talked to him a lot about</font> all the old stories from those days.