SHave smartphones have caused harm or good to society?

While it's possible to change some statements into questions simply adding question marks, that sounds awkward with this statement. Here you need to move the auxiliary verb before the subject.

It is critically important that we know how to manage the use of smartphones or, and modern technology in general.

Personally, I agrfeel that smartphones have more benefits over bad ones I feel this way for two reasons which I will explore in the following essaythan disadvantages.

If you were going to write a book, maybe it would make sense to use the structure "I'm going to tell you what I'm going to say, and then I'm going to say it." But in a short essay like this, that feels like overkill, so I removed the second sentence.

To be more specific in educational purpose, lots ofMany students nowadays rely on their mobile phones to study or review any topic they want to read.

"To be more specific in educational purpose" is just wordy and gets in the way of what you are trying to say.

Note also that "lots of" is informal, so I replaced it with "many".

I have to admit that mMy opinion on this matter has been profoundly influenced by my own experience.

"I have to admit" sounds like you're about to say something embarrassing. But that's not the case.

Six months ago, I realized that I haved to proceed with the TOEFL exam in addition to the board exam to get the chance to practice dentistry in the USA.

SoHowever, that was not a problem for me because I could downloaded my materials onto my mobile{smartphone|cell phone|mobile phone}.

Also, there are a lot of mobile apps I used to study from while I was during my free time or breaks in my work.

Furthermore, smartphones nowadays madke connections between people also easier [nowadays].

You don't necessarily need "nowadays".

Two years ago, I had to work in a city that far away from my family.

Therefore iIt was not possible to visit or see them regularly.

[The most thing that affected me most, to be honest., was my mother's cooking.]

This is the grammatical way to express what you were trying to say. But I don't understand the purpose of this sentence. Smartphones didn't make it possible for you to enjoy your mother's cooking. So how does this relate to your main argument?

My mother's cook So, the presences of sSmartphones solved this issue.

I used to spend lots of time on video calls talking with my mother and all my family.

This sentence doesn't belong here. Did you copy it and then forget to remove this instance?

Therefore, iIt was not possible to visit or see themmy family regularly.

The most thing that affected me, to be honest.

Why are you using "to be honest" again within the space of only a few sentences? It's a phrase that should only be used sparingly.

My mother not being around.

This was not a sentence, so it would have to be fixed. But I think it should be removed altogether.

So, the presence of smartphones solved this issue as well.

You could say "the existence of smartphones" rather than "the presence of smartphones". But "smartphones" is more succinct.

I used tocould spend lots of time on video calls talking with my mother and all my other family members.

Moreover, wWith this technology, you can feel that you are actually in the exactsame place as other people, so I used to do this to not feel lonely at mealtimes.

In conclusion.

This is not a complete sentence. Furthermore, I think it's better to leave it out.

because ofFor the two reasons I have mentioned, I strongly believe that smartphones have caused more benefits rather than harming to our society.

This is because it allows us toey can be used it forn various beneficial ways, including for education and communication purposes.