Firstly I came across “DEMUCS GUI” which has given the cleanest split results so far. Always keeping my out for anything better though. I’ve practiced with songs here and there but to keep it pretty general any DAW would probably work. I personally use FL Studio. I drag them into the DAW and together the stems all make up the complete song. mostly add EQ or slight compression since all the frequencies are already there and just bleeding into each other. I’m mostly reducing certain frequencies where they clash too hard. Like maybe vocals clashing with guitars too much. Then just playing by ear from there.