This exports an array of numbers to the file out.dat.
Here are the contents of the file out.dat.
This imports the contents of out.dat as a table of data.
Import["file","Table"] will handle many kinds of tabular data, automatically deducing the details of the format whenever possible. Export["file",list,"Table"] writes out data separated by tabs, with numbers given in C or Fortran‐like form, as in 2.3E5 and so on.