Your visual library is basically a series of images that you have stored somewhere: in your head, in a folder of printouts, inside your computer or your phone. It should be very well organized by category and cover such things as you need for your artwork: people (with and without clothing) costumes, jewellery, hats, animals, plants, cities, technology, nature, other artists' work that you're inspired by, and anything else that could be useful for you to create your own stuff. Here's a more detailed answer:
https://graphicdesign.stackexchange.com/questions/16405/what-is-a-visual-library-and-how-to-work-on-it
Start small. Practice spheres, cubes, cylinders, and pyramids. Then add some household objects: vases, plates, cups, fruit, shoes, anything you see around you. Don't forget to collect colours, textures, and patterns you find interesting. Look at lots of other artists work - which paintings resonate most with you, what do you want your own paintings to look like? Later as you grow as an artist you'll be able to draw almost anything you like from your own imagination! But it is a long process that takes a lot of time to master.
Useful playlist
https://www.youtube.com/watch?v=sY_eAR0HKus&list=PL10e8sNDisIgabTnynm1w2UG8DYGEMTXA
Useful free tutorial from Norwegian character artist Even Amundsen. It covers developing your visual library and studying from references before applying what you've learned to the final piece.
https://cubebrush.co/evenamundsen/products/bucmw/process-dwarf-physician-tegn-assignment