Concord is a program which makes a concordance using plain text or web text files.
To use it you will specify a search word or phrase, which Concord will seek in all the text files you have chosen. It will then present a concordance display, and give you access to information about collocates of the search word, dispersion plots showing where the search word came in each file, cluster analyses showing repeated clusters of words (phrases) etc.
The point of it…
The point of a concordance is to be able to see lots of examples of a word or phrase, in their contexts. You get a much better idea of the use of a word by seeing lots of examples of it, and it's by seeing or hearing new words in context lots of times that you come to grasp the meaning of most of the words in your native language. It's by seeing the contexts that you get a better idea about how to use the new word yourself. A dictionary can tell you the meanings but it's not much good at showing you how to use the word.
Language students can use a concordancer to find out how to use a word or phrase, or to find out which other words belong with a word they want to use. For example, it's through using a concordancer that you could find out that in academic writing, a paper can describe, claim, or show, though it doesn't believe or want (*this paper wants to prove that ...).
Language teachers can use the concordancer to find similar patterns so as to help their students. They can also use Concord to help produce vocabulary exercises, by choosing two or three search-words, blanking them out, then printing.
Researchers can use a concordancer, for example when searching through a database of hospital accident records, to see whether fracture is associated with fall, grease, ladder. Or to examine historical documents to find all the references to land ownership.