Help with stitch library

Hello All:

I bet this is an easy one, but it is definately over my head. Using the stich library how do you determine how many stitches to cast on. For example the seafoam stitch I want to use for this blanket requires 10st +6. What does that mean. Does that mean you decide how many stitches you want to cast on and make sure it is divisible by 10 and then add 6 to it or do you make sure your cast on stitches is divisible by 16. Thank you for all your help.

yup so if you wanted 4 pattern repeats (or whatever your stitch is requiring) you would cast on 40 stitches plus 6 more so 46 stitches. Generally i think those extra stitches are going to be an extra three on each end for selvidge but not always i am sure.