The embroidery thread for cross stitch is
called stranded cotton. This is because the thread is made up of separate
strands, normally 6 in total and usually sold as an 8 meter length bundled
into what is known as a skein. (stranded cotton is sometimes sold by the
metre and can also be bought on 50 metre cones.)
When you stitch a cross stitch pattern the
instructions will tell you how many strands of thread is needed for each
type of stitch. To separate the strands, I find the best way is to
hold the length of stranded cotton in my left hand (with my thumb and
forefinger), then with my right hand, gently pull one strand out from the
length of thread. If two strands are required you can either use the
one strand and double it over, to use the loop knot method of starting of,
or pull another strand out of the length of thread and place them together.
Don't be tempted to pull two strands of thread out together they will not
lie neatly when being stitched.
As a general rule,
you should separate two of the six strands to stitch cross stitches
and separate one strand for back stitch.