There are 2 types of octahedron commonly available. One is a Face Turning Octahedron (FTO). This one you rotate a complete face to make turns. The other is a corner turning one. That one you rotate the top pyramid of 4 triangles to a face, leaving the base.
Not sure how to solve an FTO, but there are guides on youtube. Should be easy to find now you know what it's called.