Forum:Best way/raids and missions to get better cr

I was wondering what are the best missions to get good gear I am at 100 cr with all the "traces in time" gear thanks to this event to advance character cr but while I haven't looked at all the iconic equipment, what I have seen isn't as good as what I have so I was wondering what exactly do I need to do to get better gear and if possible preferably for a dps atomic character. Also I don't quite understand what people mean when they say do the raids so if anyone could explain more that would be appreciated.