Microsoft 365 via a licence card: Go to the www.microsoft365.com/setup webpage and sign into Microsoft account, enter the product key (scratch off the silver covering) and download and install the apps. Open Start menu and search e.g. Outlook then click ‘Pin to taskbar’

Microsoft 365 licence via Microsoft Account: Sign into Microsoft Account (account.microsoft.com) and go to Microsoft 365 and buy a new licence or download from an existing one as required

Other software installation: Go to the relevant webpage then download and install as instructed