There Are Three Things That Happened Today

First:

Now I have friends on italki O(∩_∩)O哈哈. One is a boy, the others are girls (Is there more than one girl?). I'm so happy, thank all of you!
Second:

Even though my grandma has been ill, she is feeling better today. She is so kind to me, I hope she will be okay. (both ok and okay are correct, but okay looks better to me and seems more appropriate considering the nature of what you said.) Glad to hear your grandma is getting better :). 
Third:

My sis and I bought some cosmetics, but we don't know how to use them. We have to study how to do make-up ourselves. ↖(^ω^)↗加油.

Very good!  Nearly everything your wrote was correct in every way except formatting.  So I just changed the formatting around, capitalized what needed to be capitalized, (something you would do well to focus on), and changed a few word forms.

About spacing and capitalization:  The first letter of the first word of every sentence should be capitalized. The same goes for every occurance of the pronoun "I" (I, I'm).  There should always be a space after a comma (I know that that is a little bit more difficult with a pinyin keyboard, presuming that is what you are using of course.)

加油！

There are three things which happened today.

Firstly, I have friends on Italki, O(∩_∩)O哈哈~ ((哈哈 is translated as 'Haha!', I think)); one is a boy, the others are girls; I'm so happy! Thank you all!
Secondly: after my grandma being ill recently, she feel better today; she is so kind to me... I hope she will be OK.
Thirdly: My sis[ter] and I bought some cosmetics (('Make up' would be more suited here)), but we don't know how to use them; we have to study how to use make-up ourselves,↖(^ω^)↗加油. ((Not sure what 加油 means))

((Good for you! A fairly good entry; work on your capital letters and sentence structure. A good entry nevertheless!))

There are three things happened today

first: Now,i have friends on italki,O(∩_∩)O哈哈~,one is a boy, the other is a  girl,i'm so happy,thank all of you! 
second:even though my grandma has been ill,she feels better today , she is so kind to me,i hope she will be ok. 
third:my sis and i bought some cosmetics,but we don't know how to use them,we have to study how to make-up ourselves,↖(^ω^)↗加油.