You need to first join the conference (see how here) and then choose the conference you want to submit your paper to:
If you cannot see your conference in the dropdown menu above, you need to join the conference first by going to Conferences --> All Conferences:
Find your conference, and click Join, then you should be able to see your conference in dropdown menu:
Then, you can submit your paper by clicking the Submit Paper button on the dashboard:
Or go to Submission --> Add Submissions
Then, follow the instructions on the page to submit your paper!