When you say project, do you mean NSF (or similar) funded project? Then make a poster based on the solicitation you send to NSF. Otherwise, imagine that you want to persuade a funding agency to give you money. You will have to explain what you are going to do and why it is interesting. That's what your poster is about.
You should be able to find old posters lying or hanging around to give you some idea how they work. Usually, posters try to convey information in too much detail and are therefore hard to read. A good poster makes it easy to see (not at one glance but within a few seconds) where the project is located in the spectrum of your discipline. In the case of a project you need to tell what it is and why it is important. You also need to say how it is going to be attacked. Do not assume that viewers know too much about your field, but do not assume either that you need to explain electromagnetism either. If you can, a good illustration spares many words.