Glow berries are one of the many new items added with the recent update for Minecraft 1.17, and the player can find and grow them by gathering them up from lush caves.
However, before going off to look for a lush cave, please note that both lush caves and glow berries are not in the main branch of the game yet. Both should arrive later this year in update 1.18, and when that happens, this method will work, but it will not work for branch 1.17.
Related: How to find Lush Caves in Minecraft
That said to grow glow berries, you will first need to find them. You can find the berries growing inside lush caves in the game. To find lush caves, simply search for Azalea tree, as they will grow above lush cave biomes.
Once you locate the tree, dig around or look for a cavern, and inside you can find the glow berries growing.
Gather them up, and you can then grow them by placing the plant on the bottom of a block in the game. The plant over time will grow and extend to eventually spawn berries on one of the vines.
Along with that, you can also use these glow berries as an organic light source as they will glow with a light strength of 14. You can also speed the growing process of glow berries by using bone marrow on them.