Will is a form of to be, while going to is a form of go to.
It depends on how it is needed to be used!
"I will find the shoes!"
Here, only will can be used, unless you add "am" (another form of to be), then you can use going to.
"I am going to find the shoes!"
"I am going to the store."
Same concept here!
"I will go to the store."
Will is a to be action, so it's anything you can do.
Going to is a directional action, so it only applies when you are going somewhere.
Sometimes you need to use both in the same sentence!