It is possible to learn how to sail by banging it out on a small sailboat until you can get it to go. Also learning from others casually on the dock can be fine. However bad habits that you can get away with on the small boats translate in to dangerous problems when the size of the vessel, and the forces exerted on it increase. Winch control, sail trim, jibing safely, rules of the road, and crew overboard drills are important areas covered in basic sailing courses.
Text books for sailing schools, ASA, U.S. Sailing, etc. are available online, these will give you a good guideline for terminology and theory, however, practical on the water time with a competent instructor in invaluable. Take the time to learn properly from a reputable school they will give you the skills and confidence to take your family sailing safely. when looking at schools find out how much time you will spend on the water not just how much the course costs. Some schools offer quicky two day basic courses that while giving you an intro into the basics don't really give you the opportunity develope, and practice new concepts. Will you be able to recover a person in the water by yourself in varied conditions? Safely sail the boat back to the dock when, not if, the motor fails? and many other what if's that should be easily at your command at the end of a basic course.
Sailing is a wonderful way to spend your time (life), and confidence in your abilities comes with, knowledge and practice. Starting with a solid instructional base will give you the tools to develope as a competant sailor