Viva Nigeria! It’s great to read about the popularity of Fortran with professors in colleges there.
Re: Fortran 2018 vs previous versions, you may note the thinking now appears to be more in terms of modern Fortran as signifying versions since Fortran 90 revision or since 2003 depending on the person. And to start with ‘modern Fortran’ generally.
So you will see a lot of books use the term ‘modern Fortran’ in the title - see this link by @milancurcic, one of the founders of this site for a great new book on Fortran which you can start learning without any background in prior versions of Fortran.
There are other books also such as by Chapman; by Metcalf et al.
And you may want to keep in mind short video tutorials on YouTube in conjunction with open-source (free) development tools such as gfortran with Code::Blocks:
