To start painting you will need to click on an easel.
If you are already in the painter career then you have a couple of other options to get inspired as you progress through the career – research an art reference (at the computer under the web research section), and critically assess, or gather inspiration (both from a painting) Starting Painting To get inspired your sim could take a thoughtful shower, browse art on the computer (under the web section), cloud or star gaze (with the Outdoor Retreat Game Pack), admire art (with the Art Lover trait), listen deeply to music (with the Music Lover trait), or analyze a book (with the Bookworm trait). The more inspired your sim is the faster they learn and the higher the chance of producing a higher level painting, so ideally you want to try and get your sim very inspired as often as possible. You will want your sim to be inspired or very inspired whenever they paint, as it will not only boost the speed in which they learn the painting skill, but increase their chances of painting a painting of higher quality. This is a step by step guide on completing the aspiration if you would like advice on choosing traits and setting up to best complete the aspiration please read the previous post here.