Danish has two relative pronouns - som and der. The translation of der or som will be that, who or which. They have the same meaning and are used for describing nominal elements with a subordinate clause:
Jeg mødte en mand, der/som var ude at gå med sin hund. (I met a man who was out walking his dog)
But the use of der is restricted: Der can only be used as subject in the subordinate clause. And der has to come immediately after the word it is describing:
Jeg har en hund, der/som elsker øl. (I have a dog that loves beer) vs. Jeg har en hund, som du godt må få. (I have a dog that you may have)
Jeg har en hund, der/som elsker øl, og som hele tiden vil ud at gå.
So if you want to play it safe: always use som.
Choose der/som or som in the drop down list.