"help out" can be interchangeable with help in some instances, but not all I think. I can help with your question. I can help out with your question. I can help with answers. I would like to get some "help" but I would not need "help out" unless I am inside of something that restricts me. Would you like more help? Perhaps someone else can help you. Perhaps someone else can help out. So you see that "help out" can refer sometimes, to circumstances of "restriction". If you are not physically restricted, "help out" will not always apply. Would you like for me to help you out? I can give you a hand if you like. I like to help out. I like to help others. Do you want some help? We can both help if anyone has a question. [Basically, "help out" is mostly Idiomatic. In other words, you can simply forget about ever using it. It poses a difficulty. If you simply restrict your use to "help" you will find your communications easy and not at all problematic.]

The difference is very subtle. When you ask someone to help you, you can do what you need to do on your own, but help would be nice. When you ask someone to help you out, it sounds more like you Really need assistance. However, like you said, you CAN use them interchangeably in some situations: "Is there anything I can do to help?" .... "Is there anything I can do to help out?" "She helped with..." ....... "She helped out with..." "He helped by doing..." ... "He helped out by doing.."