How to create a time logging app?

I want to create a Timesheet application.
user should be able to register, login
can create time sheet
each time sheet have list of task with start and end time etc.
user should be able to see his own time sheet.

I have setup frappe with frappe_docker not user where to start how to create.

Check the Projects modules, there are existing features already there. Might be useful in your project instead of doing from the scratch

you mean in ERPNext or in frappe?

It is in ERPNExt. Frappe is the framework, while ERPNext are actual applications running on frappe.

I agree with @ozner102 that the Projects module would be the easiest approach for this. You can obviously customize it to your own needs.