Gallifreyan is a form of artistic writing seen in Doctor Who, however in the show it almost always has no meaning (with one exception, the 15th Doctor's sonic screwdriver). Because people wanted to write in Gallifreyan, there have been many fan-made systems to create actual Gallifreyan writing systems with meanings. Gallifreyan can be thought of as either an artistic alphabetic/abugidic writing system, typically written in a circular fashion, though it may sometimes be written linearly. The most famous form of Gallifreyan is sherman's/Circular Gallifreyan.
For that, I need to refer you to this guide. But for the short answer, a big circle with little circles in it is a sentence circle, each one typically showing one sentence. There will usually be a smaller circle in it with dots and lines on it for punctuation. Then are word circles, which are small circles with circular cutouts/circles added on to represent consonants, with lines and dots clarifying which specific consonants. In these consonants are smaller circles with lines representing vowels. That is pretty much it.
Yes, I do! I post my artworks on my Tumblr and take commissions at my Ko-Fi and Artistree. If you are curious for an artwork, check these out! Some of my designs can be seen below: