Welcome to the Ranch.
Java has two kinds of types: primitive types and reference types. There's a limited set of primitive types: byte, short, int, long, boolean, float, double, char
Primitive types are not objects. Things like collection classes (for example ArrayList) can only store objects. To make it possible to store for example simple numbers in an ArrayList, these numbers (of type int, for example) must be wrapped into objects. That's what the wrapper classes are for. For each primtive type, there's a corresponding wrapper class: byte -> java.lang.Byte, short -> java.lang.Short, int -> java.lang.Integer, etc.
Java can automatically convert primitive values to and from instances of the wrapper classes, which makes the syntax more convenient (you don't have to do these conversions yourself all the time).
Oracle has a tutorial about this subject:
Autoboxing and Unboxing