It is a charming first attempt. To be honest, it's bad, but compared to other people's first time, this is better than most. It is fine that it's bad. Everyone's first attempt is bad, one day you will look at this and feel embarrassed on your own. Now, don't worry about anything else and just finish the story. Once you have finished it, you can rewrite it and make it better or you can use the experience you got from writing this, into writing other stories.
Don't be too ambitious and make like 100 chapter stories or something, though. You don't want to continue this for too long. It's your learning experience, don't go overboard. 20 chapters should be more than enough, though Ai-chan would suggest 10.
That being said, if you want to improve:
1. Punctuation
Reread your work and add punctuations wherever needed. Many of your sentences didn't have full stops.
2. More description would make it better.
3. You often write the dialogue and the speaker on different lines. While there are writing styles that does this (Ai-chan also sometimes does it).
"MAMA'S HOME"
I yelled before crashing into the legs of said person.
But in this case, you want it on the same line. Also, punctuation.
" Already home?"
A girl in an apron and a wooden spoon in hand greeted mama, that is my second big sister, Mira, she was a lot like our mother but with black short hair and ears matching color instead.
This is fine, but you should add the speaker on the same line, such as ["Already home?" the voice of a young girl in her teens came out from the kitchen.]
4. Grammar
A girl in an apron and a wooden spoon in hand greeted mama, that is my second big sister, Mira, she was a lot like our mother but with black short hair and ears matching color instead.
But watch the punctuation and the tenses. In one sentence, you use past tense, then another present tence, then past tense again. While it's not like you absolutely have to use the same tenses in the same paragraph, you should at least keep your storytelling in mind. You are telling this story in past tense, aren't you? It should instead be
A girl in an apron and a wooden spoon in hand greeted mama. She was my second big sister, Mira. She was a lot like our mother but with short black hair and ears matching color instead.
Ai-chan underlined the word that Ai-chan didn't understand what you were trying to say. Is it black hair and ears having the same colour? Is it the ears having the same colour as your mother? Does it mean your mother has black hair and ears?
