What's the difference between join and join in? I am really confused.

Childhood I miss my childhood, I miss watching the leaves fell from trees, I miss growing flowers with my grandparents, and I miss playing with my cousin who lived just a few metres away from my door. But now, I am stuck in my room dealing with homework, I can even use my textbooks to build a hill. When I was in kindergarten, my parents built another house in another town for my grandparents, and they took me away since I was the only grandchild in the family. Well, at first I had no friends, then my grandfather took me to my cousin, we got along very well. I remember I was the protective elder. He always told me my neighbour next door always bully him, so everytime I passed their door, I would always glare at her, which I thought I was very brave lol. But I never thought that the little girl would be my classmate and best friend in the future. I was having a great time, I enjoyed staying with my grandparents, I helped my grandmother do some housework, and grew flowers with my grandfather. I didn't miss my parents at all, they were like strangers to me. When they took me to visit my parents, I could barely say a word to them. I was too shy to do that. But my grandfather sometimes got drunk. He loved drinking and smoking. And everytime he was drunk, he would have a fight with my grandmother, I just had to watch it in the corner, watch my grandmother crying over and over again. Luckily, he stops drinking and smoking now. Unfortunately, he does that only because he can't, he has esophagus cancer now. Well that was my childhood. I know I am pretty lame at writing :(

min introduksjon Hei! Jeg kommer fra Kina. Og jeg er bare 14 år gammel, min favorittmusiker er Kygo, AURORA og astrid s. Jeg elsker å se Skam. Jeg elsker Norge, men min norsk er dårlig. Jeg har lyst til dere å hjelpe meg. Jeg kan hjelpe deg med dine kinesisk hvis du vil.