Make yourself a team, with only yourself in it, and then just choose level and go... I really wish people would actually pay attention to the Runescape tutorials that they give instead of just clicking through it to get to the thing....
Click on your ring of kinship. An interface will pop up, click form party. After this, go down the ladder by the fremennik banker. It will prompt you to choose a floor, which complexity you want to play at, and the dungeon size. The dungeon will now start.