When a pattern directs to "ease" or "ease in," you are generally sewing a
longer piece of fabric to a shorter piece or a curved piece to a
straight piece. This creates shape in a garment or object without pleats
or gathers. To ease, match the ends or notches of the uneven section
and pin together (or pin as instructed by the pattern). Continue to pin
the remaining fabric together, distributing the extra fullness evenly,
but making sure that the seamlines match up as smoothly as possible (you
will be smoothing the excess fullness away from the edge); don't be
afraid to use a lot of pins. Stitch slowly, smoothing as necessary to
ease the pieces together as evenly as possible, being careful not to
catch tucks in the seam.