Bluegrass music is defined many different ways. I think of it as a type of singing (3-part old-time or modal style harmonies) combined with acoustic instruments. Of course, as with any dividing line, the border is fractal and can include lots of stuff that doesn't have harmony (or even singing) and can use a wide variety of instruments (and may not even include the mandolin or banjo which many folks regard as required for bluegrass because the sound was created by Bill Monroe on mandolin and didn't really coalesce until he got Earl Scruggs on the banjo).
Anyway, there are a bunch of different ways to play the banjo, and the bluegrass rolls form the basis of most modern banjo-picking.
Many folks start right off showing people the "back-and-forth" roll: Alternating Thumb and Index or Middle finger.
That is an excellent way of playing the banjo (or any other stringed instrument, but it isn't really a roll that provides syncopation (or even requires the use of three fingers)). And an alternate name for bluegrass picking is Scruggs-style or Three-finger picking.
I always start off with the roll. It takes longer to get started to where your practicing can sound like a song, but
Bluegrass banjo players almost always use fingerpicks. They provide a louder sound and seem to move smoother. You can play without them, but at the expense of losing sound or speed. That's something you can get around thru practice, making a dedicated effort to practice being loud and smooth while playing without fingerpicks.
I highly recommend at least trying them. They are uncomfortable at first, but you quickly get used to them. On the other hand, if you use them, then you can't quickly switch to frailing in the middle of a song, and they are something you can lose.
The basic setup is Three finger picks: one is a thumbpick (usually plastic but they make metal ones), and two fingerpicks (usually metal but there are plastic ones), one each on the Index and Middle fingers.
Many people say you need to have the other two fingers, the Ring and Little, anchored on the banjo head. That also is optional but should at least be explored as an option.
|Basic Forward Roll
Bile Dem Cabbage Down
|Mama Don't Allow
Modifications to the Roll
|Thinking About the Forward Roll
Grandfather's Clock w/Chimes
|Rolls with Scales
|Intro to Licks
|Forward Roll Variations
|The Square Roll|
Bile Dem Cabbage
|Skip to My Lou/
|The Reverse Roll
Bile w/Full Chords
|Mixing It Up
Bile w/Full Chords