I will attempt to explain it super-easily. You will find a bunch of RS gold dungeons, known as floors. Consider these as mazes that you get XP for by reaching the finish. Since you level the skill, you unlock more flooring. The floor number has nothing to do with how tough the dungeon is. The only difference between every floor is that the boss appears different and the scenery changes.
The sophistication determines how tough the floor is, and also the size determines how long it will take to complete. Both are determined by the party boss. Everyone selects complexity 6 since you get the most XP like that. The size (the number of rooms there are), again, depends on what the party leader selects. When there's 5 people in your party, expect it to be set on big and require a very long time to finish.
After you complete a floor for the first time you get double XP. The second time you only get half. This is called prestige, however you can acquire double XP again in the event that you click on the reset button. So, everyone does all of the floors they have unlocked once Like floors 1 - 27, clicks the refresh button, does floors 1 - 29, (because they lvled dungeoneering by completing dungeons), clicks reset again, and it keeps going like this. Try not to perish as it enhances the XP you get.
If you are F2P some of the rooms are members only doors. They aren't unlockable so don't worry about them. If you need any help on the puzzles, then ask the people in your party or assess Rs Wikia. They have an awesome puzzle manual.
Play dugeoneering on the official world. I think that it's world 7. Furthermore, if a person is spamming about how they have the flooring you need, click trade on them. That usually means you need them to send you a request to join their celebration. If you want to buy OSRS gold switch from melee to stove or to magic, solo a sophistication 1 floor. You don't even have to finish it. Simply bind (makes it so you've got that thing in your stock every time mechanically ) the thing (s) you need and stop. Whenever you've got a minimal dungeoneering level you're allowed to have 1 weapon or piece of armor and 125 of one type of rune or arrow.