You mean the Crossing the Chasm mission? You just do it. It requires a little bit of skill.
If you are not allowed to start the mission, then probably you don't have enough energy. Wait a couple of hours, for your mist energy to build up, and then try again. If someone else is playing Spiral Knights on the same computer, then don't let them play for those couple of hours. All free Spiral Knights accounts on a single computer share the same mist energy stream, which is what you're using to let you play the mission.
You mean the Crossing the Chasm mission? You just do it. It requires a little bit of skill.
If you are not allowed to start the mission, then probably you don't have enough energy. Wait a couple of hours, for your mist energy to build up, and then try again. If someone else is playing Spiral Knights on the same computer, then don't let them play for those couple of hours. All free Spiral Knights accounts on a single computer share the same mist energy stream, which is what you're using to let you play the mission.