It depends on the topic. "You can help many places" is not "wrong" exactly, it depends on the intention behind it. For example, you could say: "By giving money to an international charity, you could help many places around the world." "You could help many places around the world by donating to an international charity." In itself it is not "wrong", it depends on the context. You could not say: "I want you to work for this man, you could help many places." If you meant: "I want you to work for this man, you could help in many places." Meaning: "I want you to work for this man, you could help in many ways." "I want you to work for this man, you could help him with many things." VS "You could help many places across the country, doing volunteer work." Meaning: "You could assist several locations across the country, doing volunteer work." I hope that helps.

By itself, without context, "You can help IN many places" is correct. "You can BE OF help at many places" will be correct.