There is something I don't understand now...
What is the difference between these two letters??

I know this one is つ　tu
But what is this smaller one っ? I can't find it on the keyboard..
Just like the one in mikka , yokka.
みっか
よっか

And check out this Power Point work by me, I have just made it now.
1. Days of the Month - From 1st to 10th.pptx

I also made a way to memorize the days from 11th to 19th, pretty easy I think and if you saw it as well, Sumippi, I hope it will be of help to you so you don't get confused.

The days from 11th to 19th starts with juu and ends in nichi, except for that 14th starts in juu as well but it is just like 4th ends in yokka...
juuyokka

Let's see what we will do next...!!
Remember the song I have just made..
(san - shi - goga - roku - shichi - hachi - kuga)
(1) Now remove shi from the list.
(2) Now remove ga from goga, and remove ga from kuga.

Days of 11th and 12th
11th : We will add ichi from January or it's just number 1 ichi ichigatsu, we will just add it after juu.
juuichinichi.

12th : We will add ni from February or it's just number 2 nigatsu, and we will just add it after juu,
juuninichi.

Now the rest in the list of the song, we will add them after juu for days of 13th to 19th except 14th in same order.

Let's try and see.
13th: juusannichi
15th: juugonichi
16th: juurokunichi
17th: juushichinichi
18th: juuhachinichi
19th: juukunichi

And here is another Power Point work by me for days from 11th to 19th this time.
2. Days of the Month - From 11th to 19th.pptx

And ohh.....!!!!
After I have discovered a new and simple way rather than this I discovered that forming Japanese numbers are so so so so easy than I expected... You don't have to be confused...
I think the only one is different is just 4---- numbers and numbers like 20, 30, 40, 50, etc.......

Hello,
Which is the correct one for number 10?
Juu or jyuu?
When I type them with keyboard I see no difference at all.

Juu: じゅう
Jyuu: じゅう

For example number 11 can I say juuichi?
In a site It's jyuuichi.
Japanese Numbers - The Number System of Japanese

Thank you for your detailed explanation...I use these expressions daily but haven't noticed any rules there...(^_^)笑

We usually write 'juu', not 'jyuu', and 'juuichi' not 'jyuuichi'...

I think you can type 'っ' with「L+T+U」.
With the key 'L', you can type smaller letters such as ゃゅょぉぇぅぃぁゎ.

if you type "yokka" (with a double k) the small tsu (っ) should pop up automatically.

If you just wanted to type っ you can type "xtu" and it should come up.

Also to note

ぁ - xa
ぃ - xi
ぅ - xu
ぇ - xe
ぉ - xo
づ - du

Thank you!
OK what about the other small letter?
ゃゅょぉぇぅぃぁゎ

Now I know that
Ltu = っ

And for number 20, can I say?
juujuu

20 = 10 + 10 = juu + juu = juujuu

I currently learned the numbers, can you check them, please?
Twenty-One: 2(10) + 1 = ni-juu-ichi
Twenty-Two: 2(10) + 2 = ni-juu-ni
Twenty-Three: 2(10) + 3 = ni-juu-san
Twenty-Four: 2(10) + 4 = ni-juu-shi
Twenty-Five: 2(10) + 5 = ni-juu-go
Twenty-Six: 2(10) + 6 = ni-juu-roku
Twenty-Seven: 2(10) + 7 = ni-juu-shichi
Twenty-Eight: 2(10) + 8 = ni-juu-hachi
Twenty-Nine: 2(10) + 9 = ni-juu-ku
Thirty: 3(10) = san-juu
Thirty-One: 3(10) + 1 = san-juu-ichi
etc....

I also have a question..
Is it September Sixth?
Shouldn't this be in Japanese...
kugatsu muika wa desu ka.
くがつむいかはですか。

In that site there is no wa after the subject here...
kugatsu muika desu ka.
How is this?
Can you explain?
Dialogue, Say It Out Loud - Lesson 5 - Language - Kids Web Japan - Web Japan

おお！I didn't know about the 'x'-key.

ゃ-- lya / xya
ゅ-- lyu / xyu
ょ-- lyo / xyo
ぉ-- lo / xo
ぇ-- le / xe
ぅ-- lu / xu
ぃ-- li / xi
ぁ-- la / xa
ゎ-- lwa / xwa

-----------------------------

＞And for number 20, can I say?　juujuu
＞20 = 10 + 10 = juu + juu = juujuu

--No, 20 is にじゅう(ni-juu). And 20th (for the day and duration) is はつか(hatsuka). We understand にじゅうにち(nijuu-nichi), but I think we usually say はつか.

------------------------------

＞I currently learned the numbers, can you check them, please?
Twenty-One: 2(10) + 1 = ni-juu-ichi
Twenty-Two: 2(10) + 2 = ni-juu-ni
Twenty-Three: 2(10) + 3 = ni-juu-san
Twenty-Four: 2(10) + 4 = ni-juu-shi
Twenty-Five: 2(10) + 5 = ni-juu-go
Twenty-Six: 2(10) + 6 = ni-juu-roku
Twenty-Seven: 2(10) + 7 = ni-juu-shichi
Twenty-Eight: 2(10) + 8 = ni-juu-hachi
Twenty-Nine: 2(10) + 9 = ni-juu-ku
Thirty: 3(10) = san-juu
Thirty-One: 3(10) + 1 = san-juu-ichi
etc....

--All correct.^^

-------------------------------

＞Is it September Sixth?
＞kugatsu muika desu ka.

--The subject 「きょうは=today」is left out here. You can also say 「きょうは、くがつむいかですか」.

You may think 「きょうは、くがつむいかですか。」(Kyou wa, kugatsu muika desu ka. ) would be grammatically correct, but we often say this without 'Kyou wa',-- because it can be implied, I think.... It depends on the context, though.

Hello,
The subject is not "today" here. It refers to the birthday...
A: When is your birthday?
B: My birthday is September third.
A: Is it September sixth?

So, I am going to follow the correct grammar which is first comes the subject..

A: anata no tanjoubi wa itsu desu ka.
あなたのたんじょうびはいつですか。

B: watashi no tanjoubi kugatsu mikka desu.
わたしのたんじょうびくがつみっかです。

A: tanjoubi wa kugatsu mikka desu ka.
たんじょうびはくがつみっかですか。

But in the website, they didn't mention "your" in 1st A.
A: Tanjoubi wa itsu desu ka.

And they didn't mention "My " in B.
B: Tanjoobi wa kugatsu mikka desu.

And where is the subject in the 2nd A.
The website's answer is:
A: kugatsu mikka desu ka.

So, is any of my answers wrong, please?

There is no "your" and "my" because it is obvious in Japanese who you are talking about. Any unnecessary or obvious information is dropped. That is why "you" is rarely used, as 99% of the time it is obvious.

So, my sentences are correct or wrong??

Also,
A: Is it September Sixth?
kugatsu muika desu ka.

B: No, it isn't the sixth, it's the third.
iie, muika dewa arimasen. Mikka desu.

Can you tell me, what does dewa arimasen mean?

I think you are heading down a path of serious frustration, as I think you are getting way too far ahead of yourself. Along with learning Japanese, you need to learn about Japanese.

Language is not like math. Right and wrong are not so black and white. I cannot say your sentences are wrong, as they are grammatically correct, but I cannot say they are right, as no one speaks like that.

Japanese is not structured like English. Piecemealing this understanding through questions on this forum is going to be frustrating to you and tiring for us. Please invest in a good textbook or class that includes more than just grammar lessons, but "theory" and cultural understanding as well.