Q.What Is This Green Plant?
What’s this green plant? How to plant it or maintain it? Do I need to change a pot to a bigger one or plant it in the garden? Thanks.

Certified GKH Gardening Expert
That appears to be a bean of some sort, though it is still quite young. Most beans can be planted when the soil temperatures stay around 65 degrees or higher. If it is below that in your area, at night, then I would not plant yet.
Another thing to consider is that beans will not like to be moved, or transplanted. It is important to start them where you intend to finish them. You can still transplant, if you are very careful not to disturb anything, but you should expect some transplant shock.
Here is an article that will help you with beans:
https://www.gardeningknowhow.com/edible/vegetables/beans/tips-for-growing-beans.htm