I recently came across an app called "Vectornator" while browsing the app store on my Ipad. I've used vector based progams before such as Adobe Illustrator and Inkscape, but after playing around with Vectornator and watching a few videos on YouTube, I have to say I'm extremely impressed with Vectornator. The UI is much more intuitive than other programs, and the amount of resources and support available for the app are amazing. The app is extremely accessible to beginners and is also free.
Here are some abstract designs that I came up with after experimenting with the app for a bit:
