These might help:
https://www.cryptocompare.com/mining/guides/how-to-mine-nxt/
https://staking.com/nxt/
https://www.reddit.com/r/Ardor/comments/7n5yyo/complete_guide_to_forging_with_a_raspberry_pi/

I haven't tried forging. You need to open your node all the time in the network just like mining POW Chains.