A cloud-based 3d CAD/CAM package. It’s free for students, hobbyists, and startups making less than $100k/year. Extremely powerful parametric design software package. Highly recommend. You can find tutorials on YouTube as well as online courses on websites like Udemy or just wing it and learn by doing.
This is the slicing software that I use. It’s less complicated than Slic3r but still does everything I need it to do. This really comes down to personal preference, though. Also, some models are better sliced with Cura and some are better sliced with slic3r.