I need a plugin like google tasks, in which we can add in to do tasks on the wordpress page
I don’t know Google Tasks. But a Task Manager I use on nearly every blog is Cleverness To-Do List. You can order tasks by custom categories and by priority, assign tasks to specific users and set the progress for each task. Really useful, saves me hundreds of mails from my clients. ;)
You can try wp-note though it's not as close as google notebook. Because, this plugin will link your notes to posts.