To cite package ‘swirl’ in publications use:

  Kross S, Carchedi N, Bauer B, Grdina G (2020). _swirl: Learn R, in
  R_. R package version 2.4.5,
  <https://CRAN.R-project.org/package=swirl>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {swirl: Learn R, in R},
    author = {Sean Kross and Nick Carchedi and Bill Bauer and Gina Grdina},
    year = {2020},
    note = {R package version 2.4.5},
    url = {https://CRAN.R-project.org/package=swirl},
  }