What you do is cast on about 30-40 stitches, and then knit for 5 inches. Measure the number of stitches to one inch and you get whole stitches and maybe some half stitches.
This is a whole knit stitch- V
This is a half of a knit stitch- /
This is 10/5 stitches to one inch- \/\/\/\/\/\/\/\/\/\/\
You can't cast on a half stitch, but you can get x and 1/2 stitches to one inch. Does that help?