You decided to look for a better opportunity. One with a brighter future for you. And be able to elaborate a bit on that.
That's all you need to say.
1) Give it your best guess / shot now.
2) Embrace the fact that you'll always need to be learning :)
Definitely put it on your resume. Don't overexplain it in interviews. Just say that you were trying to figure out what kind of opportunity was right for you, and that this company turned out not to be what you were looking for.
Don't say that the work environment was toxic or anything like that. You should never say anything really bad about previous employers in job interviews. There's nothing to gain from that.
I believe it is still frowned upon to badmouth old employers during an interview.