The tidyselect package is the backend of functions like
dplyr::pull() as well as several tidyr verbs. It allows you to create selecting verbs that are consistent with other tidyverse packages.
To learn about tidyselect syntax as a user of dplyr or tidyr, read the Select columns section of the R4DS book.
To learn how to implement tidyselect in your own functions, read the Get started vignette.
To learn exactly how the tidyselect syntax is interpreted, read the Technical descrition vignette.