One-way ANOVA with string variables as factor

Dear all,
I want to do one-way ANOVA. I have a set of numerical and string variables.
When I want to select one of my string variables and move it to 'Factor' to do 1-way ANOVA I can't see it. I mean the string variables are not listed.
What does this mean?
Thanks for any help in advance.
I think you might need to code these as discrete numeric values rather than strings. Let's say in a study testing the effects of 3 different drugs between people, I'll create a factor (column) called "Drug" and it will take on values 0, 1, and 2, where the values might correspond to placebo, drug1, and drug2, respectively. That should work. Or a "Sex" column with values 0 and 1. etc etc.