How do i divide a dataset into training and test set

You can use the RemovePercentage filter (package weka.filters.unsupervised.instance).

In the Explorer just do the following:

• training set:
  • Load the full dataset
  • select the RemovePercentage filter in the preprocess panel
  • set the correct percentage for the split
  • apply the filter
  • save the generated data as a new file
• test set:
  • Load the full dataset (or just use undo to revert the changes to the dataset)
  • select the RemovePercentage filter if not yet selected
  • set the invertSelection property to true
  • apply the filter
  • save the generated data as new file