You open the Import Page over the Dropdown Menu under Logbook in the Navbar at the Top of the Page. Just select your ADIF/ADI File over the Button as well as the Logbook you want them in and click Import. After the File is read it will be imported to the Database, please wait until the Import is finished what is indicated by the Progressbar. When the Progressbar is Full it will let you know that you can now leave the Page.
Your QSOs are not send to external services, you can do that later from the Logbook.