If you register above with surname e.g. Dijck, van, you will be displayed in the membership list as van Dijck, but alphabetized under the D (i.e., the Dutch ordering). Registering instead as Van Dijck will put you under V (i.e., Belgian ordering).The (case-insensitive) username below is only used as login to the SPSP website, so must be unique, and rather simple to type. E.g., Kurt Gödel would sensibly choose kgodel or KurtG or so. You will need this username later to edit your details (affiliation, email address).
Below, the password needs to be contain a capital, a symbol and a number, and be at least 8 characters long.