Sure.
Basically NMZ spawns random monsters that attack you. You can use various potions that are bought with points earned inside. The two we'll worry about are Absorption and Overloads.
Absorption absorb damage done to you, instead of health. Monsters can only hit how much HP you have, not how much absorption you have. So most people who use this potion use a rock cake to get to 1 hp. This makes their absorption potions last a very long time because the monsters can only hit 1s.
Overload is a potion that constantly boosts your stats for 5 minutes, but will deplete 50 hp at the start.
The most effective way to train melee inside NMZ is dharoks, since you'll likely be at 1hp anyway you'll have a full dharoks attack bonus.
The NMZ monsters are enabled by completeing quests they show up in. Here is a picture of the best quests (easiest to hit, most xp bosses)
Screenshot - f0d759bcd4f612be56081518d78ae8cd - Gyazo
Use this guide to gear yourself. Perform some of those quests above (5) and enter the NMZ on hard mode.
Nightmare Zone/Strategies
If you're looking for a bot that will enter the NMZ for you and re supply the potions I recommend Party's
Prime NMZ bot. Otherwise my bot is free, but will not enter the NMZ for you, but most NMZ sessions last 6 hours if setup properly anyway.