If you're using RStudio, there are some clever built-in tools that ease the process:
Otherwise, in base R you have the read.table family of functions, and in the tidyverse there's the awesome readr package.
(I'm assuming you're reading in something rectangular... if not, then I'd start with readr. It mostly wraps base R functions for reading in arbitrary text, but I find its interface nicer to use and the documentation more pleasant to read)