Because of the size of the field that baseball is played on, the use of a softball would be irrational.
It depends on the age. Younger girls use a 10 inch glove, older girls use at least a 12 inch glove.
The materials you use in softball is pretty basic. You need an open area, a bat, a glove, a mouthguard, a bag or something to keep your supplies in, a uniform, and some players.
a bat, a glove and a helment. that is it.
About a 12in glove will do fine, i use a 14" but i feel it is too big. you have to be able to get the ball out quick, and you dont want the glove so big that you cant close it completly.
A baseball outfielder glove is usually 12 1/2 to 12 3/4 inches from the tip of the index finger to the heel of the glove. A softball outfielder glove is usually 13 1/2 to 14 inches from the tip of the index finger to the heel of the glove. Since a softball is larger than a baseball, a softball glove will be larger than a baseball glove. However, this doesn't mean that you can't use a baseball glove for playing softball. It just means that you will have less margin of error when catching the softball because of the smaller pocket a baseball glove has.
You can either buy glove conditioner or use something like shaving creme. Lather the glove with the oil and then place a softball in the pocket of the glove and use a rubber band to hold the ball in place. Then you can do pretty much anything to work in the glove like sticking it under the leg of a sofa or use the glove as a base during sliding practice.
The use of a softball glove is so it does not hurt your hand when someone throws it and it is also used for an aim so you do not have to aim with your hand. ( That would look silly.)
You could technically, but a softball would not fit in a baseball glove. The slit in a baseball glove is a lot smaller than the opening in a softball catcher's mitt. It would be very hard to actually catch the ball with a baseball catcher's mitt