It depends what you mean by “Advil” (ibuprofen) and why you’re taking it, but in general:
Should you take Advil before or after eating?
For many people, Advil is taken after eating or with food to reduce stomach irritation. Taking it on an empty stomach can increase the chance of nausea, heartburn, or stomach pain.
Does timing change for pain vs fever?
If you’re taking it for pain or fever, the usual guidance is still to take it with food (or after you start eating) if you get stomach upset.
What if you were told to take it on an empty stomach?
Some people are told by a clinician or the label to take it at a specific time. If your doctor gave you instructions that differ, follow those instructions.
When should you seek help?
Stop and get medical advice if you have severe stomach pain, vomiting blood, black/tarry stools, trouble breathing, or signs of an allergic reaction.
If you tell me your age, the reason you’re taking it (fever, headache, cramps, etc.), and whether you have a history of ulcers/heartburn, I can suggest the safer timing for your situation.