I'm having some trouble understanding what it is and what it's used for,
help please and thank you? :)
help please and thank you? :)

American Baby 
z* simply means that the zvalue is associated with a specific confidence level. For example, you might want to find a confidence interval using 95%. In that case, z* = 1.96
Hope that helps
z* simply means that the zvalue is associated with a specific confidence level. For example, you might want to find a confidence interval using 95%. In that case, z* = 1.96
Hope that helps