When you create your first ad (by clicking ‘CreateNew Ad’ in the menu) you are given the opportunity to create an Account. My recommendation is that you create an account as only account members can manage their ads (i.e. amend, delete or extend).
If you don’t create an account your ad will still be taken, but it will run (unchanged) for 30 days and then be removed automatically by the site.
Membership accounts of the eShop are nothing to do with your ObedienceUK membership (i.e. you can’t sign in with your ObUK username and password).