If you'd like to learn some tunes from me and hear me talk about my general approach to fiddle playing and music, check out my course on Artistworks.
Also on the Artistworks site, you can learn bluegrass fiddle from the great Darol Anger. I was lucky enough to have Darol as a teacher too, and I continue to learn so much from him. He's one of the best out there, and always entertaining. Darol's course, like mine, features many guests (including me!). Here's a fun snippet of us interviewing each other in summer of '17.
On another great instructional website, Peghead Nation, you can learn from my other incredible mentor, Bruce Molsky. He's one of my favorite musicians to listen to, and his repertoire is full of great old-time tunes. If you're interested in old-time bowing (Round Peak style, as Bruce learned from Tommy Jarrell), this is a perfect place to get it.
If you're a beginning fiddle player, or a violinist new to "fiddling" in general, I recommend learning at Jam With Lauren. Lauren Rioux is a fantastic educator and her curriculum is straightforward and extremely helpful for fiddlers - beginning, intermediate, and beyond. Her method of teaching how to hear chords (as a foundation for learning how to back up other musicians and how to take solos and make your own variations) is the best of which I'm aware.
Best of luck in your fiddle-studying endeavors! Most importantly: have fun with it. Use it socially! Don't be afraid play publicly and with other folks--it's never too early to start jamming and never too late to keep learning. Feel free to write with questions; I will try my darnedest to get back to you eventually (but sometimes I forget)!