There are many different versions of this legend, but this is the one I learned growing up…
There once was 10 suns in the sky, causing multiple droughts, making it very difficult to survive. An archer named Hou yi then shot down 9 suns with his enchanted red bow, leaving the one we see today. To commemorate his good deed, he was named emperor. However, he was a terrible ruler, subjecting his people to tyranny. He believed he was destined to live forever and therefore, set off to find a pill for immortality. He was successful and came back with 2 pills, one for him and the other for Chang'e, his beautiful wife. However, Chang'e didn't agree with his selfish act to gain immortality so she ate both pills which sent her flying directly to the moon where she is said to still be till this day.
To celebrate the mid autumn festival, mooncakes are eaten as an offering to the moon and Chang'e. These cakes come in various sizes and colors, usually depending on which region in China they're from. One similarity they all share is the round shape of the pastry. Roundness symbolizes togetherness as families come together during the festival and admire the full moon and eat moon cakes together! Friends also send each other mooncakes to express best wishes for each other. There are many different flavors of moon cake, mixed nuts, red bean paste, lotus seed paste (my personal favorite!), snow skin, yam, and many more! They can be found in any traditional Chinese supermarket only around the time of mid autumn festival. Hopefully you can get a taste of these delicious mooncakes too!