The point of it
The idea (from Paul Raper) is to be able to follow up a collocate by requesting a new concordance based on it, in the same text files as selected for the collocate. This aids exploration of related words.
How to do it
Here is an example, where there is a collocate list relating to LADY (from Romeo and Juliet).
Select a word of interest, such as LOVE,and select Follow collocate in the Compute menu.
You will now be asked whether you want a concordance of the word selected (here LOVE) using the same text file(s). If you agree you'll also be asked whether you want to restrict the search so that it finds LOVE only in contexts similar to your previously concordance (LADY nearby). If you do want it restricted you get results like
and if not, a search on LOVE in the same text file(s):
The search is carried out on the most recently selected text files (selected using the file-choose window or by reading in a saved concordance).