[Gretl-users] JOIN function

Hi everyone, I am working on my master thesis and I have a data set in three different excel files each on different lengths that need to me merged together. I saved them as csv since I have some text variables but when trying the JOIN function I always get error. I tried joining them with matching keys 2 by 2. Is there somewhere a more detailed explanation of the join function? Thank you for your help. /Andreea