How to create a new force-sobject?

[rnng]

Hi,
I'm little in trouble.
I need to create a new record in database, but don't know which recordid I need to pass in my force-sobject in order to do this.

HTML-Code

<force-sobject id="pos" sobject="Zeiterfassung__c" recordid="new"></force-sobject>

JS-Code

save:function(e, detail){
  // add Attributes to field
  this.$.pos.fields.Tag__c = new Date();
  this.$.pos.fields.Arbeitszeit__c = 8;
  this.$.pos.save();
}

Can you help?