----------------------------------------------------- **** 手伝う - Having some problem - Knowing how to resolve it. - you can do it "partly" by yourself - Hoewever, looking for more human resource, then you can complete it faster and more efficently -> 手伝ってください。 　※ e.g. 「荷物運ぶの、手伝って。」 ----------------------------------------------------- **** 助ける - Having some problem - Not knowing how to resolve it. 　You cannot do anything alone. -> 助けてください。 ※ e.g.　「もうダメ、全然わからない。助けて!」 　　　 ----------------------------------------------------- Either would be OK in : 「荷物、重い。持てない。手伝って！／助けて！」 - Knowing how to resolve the problem.　->　手伝って - cannot carry by yourself -> 助けて

They can be used in similar contexts, but I get a different vibe from each of them. Though both 手伝う and 助ける are translated as "to help," 手伝う sounds much more neutral. I would say it's more like "assist" rather than "help." For example: 家事で手伝ってください。 "Please help (assist) me with the housework." In the case of 助ける, it sounds much more urgent and in some cases, it can mean "to rescue," rather than just "to help." For example: 事故が起こったから、怪我している人がいないように確認して、彼らを助けて下さい。"Since there has been an accident, please help them and confirm that there is no one injured. This would be an instance in which I don't think you could use 手伝う and it would be more appropriate to use 助ける. I hope this clears things up a bit. Let me know if you need further explanation.