I want to second what Gamerprinter has said. While doing most of my published work thus far in raster apps like Photoshop and ProCreate, I've had success creating artwork in Illustrator, Freehand, and Inkpad. There are even apps like Manga Studio that have strong vector sketching tools along side powerful raster drawing tools. You can make beautiful work in many different programs...the tools matter less than the artist who's using them.

That said, there's nothing so intimidating as the blank canvas, especially when the tool you intend to use on that canvas is unfamiliar to you. I'd recommend settling on a small project for yourself and attempting to complete it in the app you want to learn. Small! Nothing huge or intimidating. And there are so many great tutorials available online to teach you how to do things. Google is your friend. Try "sketching in illustrator" or "drawing with illustrator brushes", etc.

There are lots of free tutorials online, so I can't recommend paying for one unless you're sure you're getting your money's worth. That said, here is a link to an illustrator tutorial on drawing. Watch the free "intro" video...it shows a few of the things that can be accomplished in Illustrator. Mastering Brushes in Illustrator - Tuts+ Course