Restart laptop?

I have a hp laptop and when I work on things and switch it off later when I switch it on again, the browsers and so the windows are not closed when I switch off my computer and then switch it on again on restart then the windows are closed?

No, the tabs will still remain open, but this can be set in the respective browser settings. You can set whether after restarting the browser either the old session is restored, i.e. The tabs are restored, or any page opens, or that a completely new tab should simply open.