Ancestry, FamilySearch, and MyHeritage are (in my opinion) the best ways to preserve and share your family history online.
Privacy: All online family history sites respect and preserve the privacy of living individuals. Your “tree” starts with you. If your parents are living, they are only visible in the private part of your tree and not publicly. To connect to great-great-grandparents, you link from yourself to your deceased ancestors.
Ancestry and MyHeritage have individual trees. Each subscriber may have multiple personal or public trees. FamilySearch has one common tree (except the private area to protect information of living individuals.)
Cost: Ancestry has subscriptions. MyHeritage is free if your tree has fewer than X persons, then subscriptions for larger trees. FamilySearch is free.