Sorting is taking a collection of things and putting them into some specific order. For example, sorting people by age, shoes by size, strings by length, planets by mass, numbers by value.
Frequently Asked Questions about sorting
For sorting the lines of a file being read from standard input, and writing the result out to standard output, one can use the following one-liner:
puts [join [lsort [split [read stdin] \n]] \n]
Or in English: read in all the data to sort, split it into the list of units to be sorted, sort that list, join the sorted list back up in the external format, and write it out.