When I heard that, I remembered my high school life.

This doesn't sound completely natural. Maybe try saying "When I heard that, I looked back on my time in high school." To look back is to remember and think about something from the past.

There were a lot of hard incidents, and I have bothered my mother, my friends, my teacher, and many other people.

Instead of 'have bothered', you could put "I asked a lot of." You could also say, "There were a lot of hard incidents, and I made it through with the help of my mother, my friends, my teacher, and many other people."

I want to tellsay thanks forto the people who helped me.

I passed the university entrance exam!

That's a relief.

What you wrote works. In this context, it might sound more natural to say "I'm so relieved."

When I heard thate news, I remembered my high school life.

There were a lot of hard incidentships, and I have bothered my mother, my friends, my teacher, and many other people.

So, I cried because I felt various emotions.

This works here as well. An alternative could be " So I cried, because I had lots of mixed emotions."

I want to tellsay thanks forto all of the people who helped me.

I passed the university entrance exam!

There were a lot of hard incidentdifficult experiences, and I have bothered my mother, my friends, my teacher, and many other people.

So, I cried because I felt variousgot emotionsal.

I want to tell thanks forhank the people who helped me.

I passed the university entrance exam!

Although "the" is usually used for specific, already mentioned or known things, "university entrance exam" is significant enough of a thing for us to probably use a "the" anyway.

When I heard that, I remembered my high school life.

Alternatively (if the first part can be applicable): "Looking at my score, I reflected on my years back in high school."

"High school life" works fine, but I'd probably say "years in high school". "High school life" has more of a... cultural tone? It's hard to describe, but I'm imagining more of a lifestyle than a collection of specific experiences.

There were a lot of hard incidents, and I haved bothered my mother, my friends, my teacher, and many other people.

So, I cried because I felt variousa lot of emotions.

Another alternative: "So, overwhelmed with emotion, I started crying."

I want to tell thanks for peoplhank everyone who helped me.

We often just use "thank" as a verb by itself, though you could also say, "...to give thanks to everyone..."