[Grammar] Commas

I am having quite a hard time dealing with commas. I'm having a hard time determining what is parenthetical and what is not. Every time I write something, I have a lot of confusion over this. I think it's because it really seems subjective; what one person might deem necessary, someone else might deem added information. I guess I'm having an overall problem with commas, because I'm even contemplating the correctness of the sentence starting with I think and ending with added information. So, if you could not only help me with parenthetical information but also with this text that I wrote, correcting my mistakes, that would be great. Please though, tell me why I should punctuate it in the ways you say and also, if I punctuate it incorrectly, why is it incorrect?

Thanks,
Sammy

[David L.]

Your use of commas is near perfect. If the other error in punctuation had not occurred...
Look at the errors you did make:

I am having quite a hard time dealing with commas. I'm having a hard time determining what is parenthetical and what is not. Every time I write something, I have a lot of confusion over this. I think it's because it really seems subjective; what one person might deem necessary, someone else might deem added information. I guess I'm having an overall problem with commas, because I'm even contemplating the correctness of the sentence starting with, "I think", and ending with added information. So, if you could not only help me with parenthetical information but also with this text that I've written**, correcting my mistakes, that would be great. Please though, tell me why I should punctuate it in the ways you say and also, if I have punctuated it incorrectly, why is it incorrect?

** "wrote", as in your original, might well have been correct, since this passage could have been an extract from some writing you did in the past, which you are using now to illustrate your problem. However, it is obviously something that you have just written for this post.
Whether "wrote" or "written", the tense of the next verb I corrected MUST be Present Perfect tense. Can you see why?

[Sammy_]

Yes, I see what you mean, how sloppy of me. I have been focusing on parenthetical information for awhile, and I guess it's throwing me off; either that or there are several places where I could use tightening up, probably the latter. Thanks for the help though, very informative. Most people don't like getting their writing criticized or corrected, but I don't feel that way.

Thanks again,
Sammy