Though the main tasks of a bioinformatician are programming software for data-analysis, actually analyzing the data, and further research to connect the computational data and results with the biology, there is still the need to communicate. Though some of it can and will be done in writing, a single image says more than a thousand words if done right.
Graphic design is the use of techniques to guide someone through a message in a clear and concise manner. Structuring images, but also text, in a way that draws attention and is readable is more difficult than one might assume.
The amount of information, space, color, scale, direction are all factors that have to be considered when shaping the message. In addition, they need to be altered to fit the audience you are communicating towards. A patient will require a different form than a fellow researcher, even if the core message is the same.
Just as writing is an important skill to learn, so is graphic design. Especially as it can support your writing, or even work on its own. It will help with your presentations, posters, as well as organizing your information.
Great starting points for learning are Youtube, and online courses. But it also helps to simply actively think about the world and its messages around you. Think why a billboard or a poster is made in a that specific way. How does an advertisement grab your attention? Training yourself into understanding graphic design will at the very least help in seeing your own work in a similar light. In turn improving it.