What is important in an essay?

Likely a stupidly simple question, but i'm a bit lost.

I've been asked to churn out a 1000 word critique jobby as part of alternative assessment. I'm on a science based HND so our written work is pretty much always scientific/potential peer reviewed formal report standard (Ie: total absence of author opinion and perspective) and I don't think i've ever been asked for an essay before.

Given that it's due Monday, I'd rather not email the lecturer and say "So, this thing i've left to the last piss taking min, what is it?".. What are the basic 'rules' for an essay?

Do I need to reference? in text? can I reference? Am I allowed to get things flat wrong? (within reason).

Well aware i'm likely worrying over nothing, but i'm used to operating within very formal rules for uni writing, while the entire brief for this is literally one sentence.

I study an essay-based subject at uni and for an essay assignment (that we have a few months to complete) we are expected to include:
- Introduction
- Main body, 2-4 points following the PEEL structure, in-text citations to back up claims (we've been told if you weren't born with the knowledge, then you need to provide a citation)
- Conclusion
- Reference list

For an essay exam, it's the same except we don't need a reference list. It's probably best checking whether you need a reference list or if citations are fine. If you need a reference list, you'll need to check what style of referencing they want.

Thanks for that (sorry I'd meant to reply before) I'm hopefully near done, got an intro, 4 main chunks of detail a and a few 100 words conclusion/opinion. I'll likely go with a ref list and in text citations just to cover myself and it would 99% be Harvard style they'd want.

You will definitely need citations otherwise plagiarism could be an issue. Citations will count towards the word count (usually) so bear this in mind.