When creating a poster there are a few steps to take.
Decide what information will go onto the poster
Decide the layout of the poster in regards to where the information will go
Decide on the color theme of your poster
Decide on a suitable backround to complement your poster
Create a slogan for your product
Create a pre poster
Get peer reviews for your pre poster idea
Create the final draft of your poster
Next , you have to use GOOGLE DRAWINGS or A3 PAPER to make a poster for your product.
Remember to :
Sell you product
List the features
List what makes it better
Make a slogan
Some examples below -