If someone attends therapy does it mean that they are crazy?

"Crazy" isn't a professional word of any kind. People who seek therapy are exploring, investigating motives and timelines and attempting to pick up some tools that help them resolve issues or generally live a happier, healthier life.

You wouldn't (shouldn't) start climbing a mountain trail blindly - you'd consult someone who knew the terrain and weather conditions. People help people; therapy is just the professional form of that.