Hi @Buyan_Thyagarajan_P and welcome to the forum!
The ability to switch from board to list view (or vice versa) is not currently available in Asana but will be available very, very soon! See Switching from Boards to List View (and vice versa) - #269 by Marie for more information.
Also note that when you are in list view, you won’t see subtasks in the main task list by default - in order to have them show in the task list, you’ll need to attach them to the project. See How to Use Asana subtasks | Product guide • Asana Product Guide for more information.