The best place to look depends on what kind of help you need:
If you're doing research and need to know where to find a particular piece of information, or just want the answer to a trivia question, try Wikipedia:Reference desk.
Visit the Teahouse if you are a new editor looking for interactive help. Ask questions about using Wikipedia and volunteers will respond as soon as possible.
Ask about technical issues at Wikipedia:Village pump, which is a page where folks especially knowledgeable about Wikipedia hang out. The village pump is a metaphor for a place where lots of people gather to discuss interesting topics.