for the category 1M cookies,Fast Click,does it mean that i can use an autoclicker and buy buildings?im confused

https://www.speedrun.com/speedrunning/thread/6tgel

It seems you didn't notice the Game Rules before asking your question.

If you'll go to the Cookie Clicker leaderboards and click on "View rules", you can see two buttons labeled "Game Rules" and "Category Rules". "Category Rules" is selected automatically, but runners need to read the information under both buttons. If you click "Game Rules", you will find your answer:

[quote]Autoclicking is NOT allowed, even if it's a function of your mouse.[/quote]

That button really could use a better signifier...