Separating strands
Cut a working length, then pull out the number of strands your pattern calls for. Keep unused separated strands for later; prevent them from tangling.
How many strands
Lower fabric counts have bigger holes and usually need more strands to cover: a common starting point is 2 strands on 14-count Aida and 3 or more on 11-count. Your pattern’s key is the final word. See the needle and strand suggestions in the cross stitch calculator.
Because a skein holds six strands, stitching with 2 strands gives three working lengths for every length you cut. See skein of floss.