"They go tonight."
Translation:De åker i kväll.
I just want to add here that, at this point in the course, the difference between kväll and natt wasn't clear to me, as I thought they were held the same meanings as "evening" and "night", respectively. Here "They go tonight" has the recommended translation of "De åker i kväll." which was confusing because one would think they would line up. But then I learned that they don't line up precisely.
I learned that "kväll" encompasses both American evening as well as night up to about 11pm. Whereas "natt" is night that is about 11pm and after (sometimes called "late night"). So technically, kväll can reffer to a time period which can be either evening or night
You could just say vi ska på fest. With some verbs like ska and måste you can just use that verb and the motion verb is implied. Otherwise you could say gå på fest, then it’s not really the verb gå as in ”walk” but it is rather the verb you use in many expressions when you’re going to some venue, like gå på kafé/restaurang/bio etc.