Would you please tell us a little about your current skills?
Do you know the difference between a jib
and a halyard?
I was away from boats for a while (ok 20+ yrs) and took a course when I got back into it. Review of terminology, laws, Coast Guard requirements, navigation, etc.., were very helpful for me.
I also have to agree with SD that for boat handling nothing takes the place of experience, preferably with a experienced sailor along in the beginning. There is a big difference between passing the "rules of the road" section of the online course, and doing the right thing when there's a trawler bearing down on you.
The books mentioned by others are good. A more basic book if you need it would be Sailing Fundamentals by Gary Jobson, used by ASA and CG Aux.