Well, to be honest most pharmacy schools focus on your science subsections than your Writing score, so if you can get a 2+ score, you shouldn't need to worry too much (I may be overgeneralizing somewhat - it's possible some schools put more weight into the Writing section, but some schools indicate in their online FAQs that they're not too crazy about the Writing section).
The prompt is typically about a health, science, or social/political issue. Like
@capri1722 said, usually the prompt includes a statement about an issue and asks you to propose one or more solutions. For example, something like: "Physical activity levels in children have been declining in the last few decades. What solutions do you propose to this issue?"
There's this misconception you'll be advantaged if you know a lot of background information about that particular subject. That's not necessarily true - the essay graders will be looking for an ability to think critically, generate viable solutions, and provide support.
One approach would be to do the following (this will all be typed on a computer):
1. Spend up to 5 minutes brainstorming and jotting down a few ideas for solutions. Choose 2-3.
2. Write an introduction that shows you understand the problem,
why it's a problem, and how your solutions would address that issue.
3. Write 2-3 paragraphs, one for each solution. It's really, really important to provide detail here. How would your solution work? What are some pros/cons? How would you overcome any challenges or opposition?
4. Write a conclusion - it can be as short as a sentence or two, but try to state a final recommendation in a way that reflects on what you've already states (and doesn't just restate it).
5. Save the last 5 minutes for proofreading for typos, errors, and flow.
There will be a pop-up reminder when you have 5 minutes left, and it can help a lot to practice so you know what writing an essay in 30 minutes feels like. It's important to try to avoid typos and errors, but it's even more important to show you've thought critically about this issue just like you would with real-life problems you encounter in pharmacy.
🙂 Since you're limited to 30 minutes (without an ability to research the topic either!), you're not expected to be a Jane Austen or Charles Dickens. This doesn't have to be the best essay you've ever written, so my best advice is just to get pen to paper (or rather, fingers to keyboard) and start writing!