The About section is a crucial part of your LinkedIn profile. It's your opportunity to sell yourself to your audience, and you should make the most of it. Start by writing a first draft of your About section, and keep in mind the pyramid method — the most important information should be at the top.
Double down on why you're passionate about what you're doing, show the things that you do, and sell your services. Write it in the first person — a mistake that 90% of people make is that they write this in the third person — which can come across as awkward.
Make sure to add examples of your work and achievements, and use good formatting, line breaks to make it easy to read. You can manually copy and paste bullet points or do whatever you want. The length of your About section is up to you, but keep in mind that a few lines will be shown as a preview, and people can expand if they want to know more.