You may need to be a little more explicit on what you're wanting to do. Mainly, a short example with input and desired ouput would be of much help.

If by n-th column you mean the n-th character of each line, or the n-th value in a fixed length data input, you probably should have a look at unpack, perlpacktut might be a useful read.

For the ouput, it looks like a job for join.

Then as Happy-the-monk said, the not-so-easy-but-still-best-way to do it is to give it a try.