Attending a concert or watching it online (your entry is correct but sounds a little better if you use the same form "attending...watching or Attend...watch)

Some people say that is better to watch a concert online rather than attending to attend in person  (you can also use ...watching online rather than attending:  just keep the forms the same within the same clause).  because (It is better to start a new sentence as you have >2 clauses in the first part.  It is acceptable to have multiple clauses but try to avoid very long sentences if you are not fluent).  They think that it is notr worth to paying for it to attend a concert. I do not share the same idea opinion (to reflect a personal point of view) for some several/a variety of reasons.

To begin with, watching a concert online is not the same because it does not allow you to experience all that is happening around you,. I think it does not let you be part of it the event. (When the object is not clear, try to avoid using "IT".  I deleted the other sections because they are not needed.  That is, the meaning is the same without the extra words).  

Secondly, I have heard people saying that they had so much fun in the at/during a concert sharing this a moment (or an experience) with someone special and seeing things that they would have not seen online.

Finally, having the opportunity to attend to a concert allows you to see in real life the singer or the band you like to listen to.

In conclusion, if you really like the band., It it is worth to paying some money for it since you will definitely enjoy it.

Great job.  Most of my changes are not grammatical corrections but rather improvements to make it sound more natural.  

Attending a concert or watch it online

Some people say that is better to watch a concert online rather than attending because they think that it is not worth it to pay for it. I do not share the same belief for some reasons.

To begin with, watching a concert online is not the same because it does not allow you to experience all that is happening around you, I think it does not let you be part of it.

Secondly, I have heard people saying that they had so much fun in the concert sharing this moment with someone special and seeing things that they would have not seen online.

Finally, having the opportunity to attend to a concert allows you to see in real life the singer or the band you like to listen to.

In conclusion, if you really like the band. It is worth it to pay some money for it since you will definitely enjoy it.

Well done!!!!!!