After installing Endnote desktop you can create an Endnote online account from the program, choose Help > Endnote online > follow the steps to register an online account.
Combine your Endnote Desktop with Endnote Online by syncing your library. Choose Library > Sync
You can also use Endote online without having an Endnote Desktop account. Register your account on Web of Science
You need to install a plug-in for Word. You download the plug-in from your Endnote online account, choose Format > Cite While You Write Plug-in: