I'm using QGIS 3.0 with the expanded SAGA options. I created a training file in SAGA standalone that I am using, but would prefer the GRASS kappa comparasion options. I have already performed the classifications in SAGA standalone but want to use qgis. I'm just a little confused about if I'm going to perform the classification and select every band individually and if that will give me 6 outputs. It's a landsat 8 image, 30 km by 50km. If anyone knows of additional documention, tutorials about the saga toolbox within QGIS.
NASA runs online courses that use QGIS to classify Landsat imagery. Perhaps you can find some support there. Advanced Webinar: Land Cover Classification with Satellite Imagery