"Write an abstract."
It sounds like a difficult assignment, but it sounds much worse than it is. "Abstract" is a new term for something you've probably already done, even if you've never called it that before.
The first meaning of "abstract" that occurs to most people is not the one you need.
"Write an abstract" uses a different definition of the word. It doesn't mean "write abstractly" or "write without being specific." It doesn't even mean "write about abstract concepts."
"Write an abstract" is a direction to write "a summary, synopsis, digest, summation, or outline." For an abstract, you need to distill your work to its essence: What did you do, and why is it important?
Examples: Actual, Concrete Abstracts.
When UC Irvine had to close its campus because of COVID-19, the Honors Transfer Council of California published all the abstracts. You can find them here on the HTCC site, arranged in the sessions as they would have been presented. There are dozens, and they span many disciplines. You'll be able to see good examples in your subject area. (For especially good abstracts, see the page of award winners.)
How Are Abstracts Judged?
Procedures change from conference to conference, but one of the most detailed rubrics is offered by HTCC. The rubric that the UCI/HTCC Conference Committee uses to select attendees covers everything, though, and is a good guide for almost any event: https://www.honorstransfercouncil.org/abstract-scoring-rubric.
A Final Word: You're Not Alone
The professor with whom you're working or to whom you've submitted the research must serve as your mentor for the conference and can help you with your abstract. (They do not have to attend; many do, but many can't.) You may also come into the Honors Program Office for help from the Chair, but this should be in addition to working with your mentor.