A volleyball court is defined by four different kinds of lines.

Baseline-The line at each end of the court-equally distant from the net
Centerline-The line directly under the net, dividing the court into two equally sized rectangles
Sideline-Lines running at right angles to the net, connecting the baselines
Attack lines-Line on each side of the court, parallel to the net, providing a guideline for the players on
their own side of the court

If your gym does not have permanent lines for volleyball, you can create temporary lines using floor tape.