Okay, let me explain this with small words so even a 420 burn it yolo cigarette like you can understand.
If the attorney had gone for manslaughter instead of murder, the provoke would have been the lynchpin in the case. Instead, they pressed for murder, which is killing with premeditated malicious intent. In small words, if Zimmerman had went out there with a specific agenda to kill Martin or someone. Since there was no way to prove this, the verdict was not guilty. Had they gone for manslaughter it would've been a toss up.