What is the best option to test the data set of images using weka? [on hold]

I have two hundred and fifty images, and extracted the features from them and put them in an Excel file, how to use the weka program so that the first 200 images for training and the remaining fifty images for testing.

Do I put the data for two hundred images in a separate file and the data for fifty images in another file? Or do I put the data for two hundred and fifty images in the same file?. Please help me .