WEKA is a popular data-mining software which needs some formats for running machine learning models or clustering. It often needs '.arff' format to handle input data sets. In addition, you can use package manager to use several different packages.
did you look at https://www.cs.waikato.ac.nz/ml/weka/documentation.html and https://www.cs.waikato.ac.nz/ml/weka/book.html ? I've used Weka and I found the book by Witten et. al. very clear and helpful. In addition there are a number of videos on machine learning regression on YouTube.