Assess the assembled bed frame to determine if your Ikea bed frame model has a metal cross brace piece. Depending on the size of the frame, Ikea bed frames will include a long, metal beam to support the sides of the bed and the slats.
For twin and small bed frames without the middle metal beam, roll out the slats from one end of the frame to the other. Lay the wooden slats squarely on the inner ledges of the frame.
For all bed frames with a stabilizing metal beam, hook both the first and last slat onto the small plastic piece at the end of the L-shaped rail and beam. Larger frames will require two sets of wooden slats; repeat for the other side.