And just to answer the other part of your question in your comments, either you know this already, or else its not on your course yet, either way, I'm sorry about that.
If u or somebody else could just explain exactly what ψ(r) and ψ(θ, ϕ), that would be great.
The functions that are used to describe the orbitals of the electron are, because we are using a spherical co ordinate system, dependent on the variables $r, \phi, \theta $. These can be expressed as the product of two functions , one based on $r $ and the other Spherical Harmonic Functions based on ($ \phi, \theta $).
So the radial wave function is the part of the overall function that describes exactly what it says, the radial distance from the nucleus.
Functions that satisfy Laplace's Equation are often said to be harmonic, hence the name spherical harmonics.
Just bear in mind that, despite their name, they don't necessarily give you a spherical orbit, as you can see below. In this picture, $r $ is taken to be a given value.
And the first few are:
Image Source: en.citizendium.org