Great job Barbara!

Your entry was completely comprehensible, and you've even used some very advanced grammar points (especially with the verb tenses, those are tricky even for natives!) In yellow you'll find some grammar corrections, in green are more stylistic corrections - they're not really wrong, but just a liiitle weird c:

This is a topic that I truly love. I’ve been meaning to write something related to this type of art for so long, that I don’t even know where to start. Mail art refers to an exchange of letters, envelopes, stamps and any other kind of little gifts that you might want to send. In my case, everything it all began some a few years ago with a postcard from Seattle. The postcard was nothing special just the typical greeting, but for me it was so meaningful that had to reply to it, and since then, a beautiful correspondence between my friend and I started. The exchange lasted 9 months, in during which the main means of communication was were the letters. It was such marvelous time, that I will keep in my heart those memories forever. (albeit technically correct, it sounds a little weird. Personally, I'd write something like "I will cherish those memories forever") Coincidentally, at that time my friend had a strong fascination with everything related to fountain pens, inks, and papers, so it was easy for him to get engaged in this game. I remember that my envelopes used to be quite a bit girlish, with a lot of flowers, glitters, and pink everywhere. I also used to add a lot of little gifts that I knew my friend would be happy to get. But the most amusing part for me was when it was time to choose the stamp! I just loved to spend spending a long lot time at the post office choosing and buying stamps. At the same time, as since my friend was aware of my obsession with stamps he used to spoil me by letting me choose the stamps that I wanted him to buy for me directly from the website of the USA post office. (again, not technically incorrect, but I'd write "USPS's website") In summary, all these tiny details are what make is what makes (here, you're referring to "all" which is a group word and corresponds with singular "is")Art Mail beautiful. Is It's not only the letter itself but also the love, time and dedication that you put into each envelope. What happened after those 9 months? Well, we finally saw each other face to face for the first time. Can you imagine what is it like to write to someone daily, for 9 months without ever having seen not even a single picture of that person before?? ;-) 

I hope your rendezvous turned out marvelous, and best of luck with your learning! c:

Hello Hiro! Great job with the diary post, it's totally understandable and very clear! :D 

There are a few small errors, mostly with synonyms and prepositions, but I was very picky with them. If you fix those, you'll sound like a native in no time! c:

I have been looking after a 6 years old girl as a babysitter in Australia since July. (you don't have to say "as a babysitter" since it's implied by "looking after") Although I have younger siblings back in Japan, it is my first experience to look after kids. (first experience looking after kids) The purpose that I chose this job was improving my English skills. (The reason why... was to improve my English skills) The family who I work for is Australian (I work for, no need for who c;) and luckily the girl has had some asian babysitters before me, so she can understand me very well even though I have thick accent in my English. (have A thick accent in English) Basically I like kids but the girl is especially adorable for me. (Basically sounds a little odd here, maybe "in general" would work better) She is kind of wild, does not stop chatting and does not run out of energy. On the other hand she is easily scared. She can not go into a dark room by herself. (cannot is usually reserved for emphasis, most people just use can't c;)

In these days she keeps watching Harry Potter movies. (Just "these days") Literally everyday, sometimes from early mornings. (every day) She almost remember every single words the characters say and what happen next on the movie. (she almost remembers would mean that she can't quite remember the words. I believe "she remembers almost" would work better, meaning she remembers most of the words) It reminds me of my younger brother. (That instead of it, or else it sounds like you're referring to the girl as "it" :D) When he was a kid he kept watching the same movie everyday and made the other family members got sick of it. (made the other family members got sick --> made other family members get sick)

I am staying with her this whole weekends but I am going to leave this position soon for some reasons. (whole weekend, since it's only one weekend you're referring to c; "for some reasons" sounds like you don't know the reason why you're leaving. If you do know the reason but don't want to disclose it, it's better to just say "I have to leave this position" or just skip "for some reasons" as a whole) I definitely will miss her. I wish we can meet each other sometimes ninth future :) (sometime in the future* c; - she sounds delightful, and I hope you do get to meet in the future c:)

Hope this helps and best of luck!