It really depends on what you want to spend. Illustrator is the one that I use, because I’m familiar with it, but Inkscape is free and does all of the same things.
They’re all about the same level of difficulty to learn at first, (damned hard), but we have a lot of Beginner Level tutorials that will help you to get started quickly:
First step is always to read all of the great information here, provided by Glowforge:
Then if you want to get going with design and understand how to use the interface in the least amount of time possible, there are a series of short tutorials that i would take in this order:
Then if you want to get started designing your own stuff quickly, the Matrix has a lot of tutorials and video links showing the best of the tips and tricks:
For using the Glowforge:
For Using Photoshop, GIMP and Paintshop:
For using Illustrator, Inkscape, CorelDRAW and Affinity Designer:
These are good ones to start with for vector design - 2D instead of 3D.
For using Fusion 360, OnShape, Openscad, Rhino, etc. for 3D design.
You’ve got a lot of choices. Just pick one vector program and try to learn it - it doesn’t take long once you jump in. I’d probably start with Inkscape if cost is an issue, and just be sure to always specify which program you are using when you ask questions on the forum. It helps folks to give you the correct answers for what to do next.