Duolingo, Pronunciator, Mango Languages, and YiddishPOP are helpful for getting started learning Yiddish on your own, but there are also some organizations that offer Yiddish classes guided by an actual instructor. If this sounds like it is a better fit for you, then check out these organizations.
It should be noted that these organizations charge a fee for their courses and they can become quite expensive. If you are already a member or sign up for a membership you will receive a discount, however.
If the classes being held by these organizations are outside of your budget or you are not located in the vicinity of where the classes are being held, try reaching out to your local Jewish Community Center (JCC). Some JCCs host Yiddish classes of their own or will know of more localized organizations who might provide classes. Find your closest JCC here.