To be out of your element is to be uncomfortable with your environment, or someone does not belong in a specific situation, setting or group For example you travel with some people and you don't feel comfortable, so you are out of your element, it's not your place there.

A fish out of water. The fish's element is water. The fish lives in water. The fish lives in its element. Get the picture here? We all live in our element.... The fish is out of its element. It is lost, struggling, almost dying. That is its meaning.

You do not understand the subject.

It means that you are in situation of which you have no knowledge or previous experience, a situation in which you feel uncomfortable with your surroundings. "I usually teach high school students. When they put me in charge of the pre-schoolers at the picnic, I felt out of my element." "He felt out of his element in a non-English speaking country."