Designing publications and posters

Try this:

Canva – a free alternative to MS Office and Adobe. It is designed to be easy to use. Here are two examples made with Canva.

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Photo of ceramic snowballs
Poster made using Canva.com

Photo of 2 people with 'Ask Me About' badges
Poster made using Canva.com. Photo by Rose Atkinson, Crown copyright
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InDesign – part of the Adobe Creative Cloud suite of tools. There is a charge for this software and you can taking training on using it. I found taking a training course with an expert to be most useful as this is a professional tool.