Busking is singing or playing music on the streets for tips.
In this case, with a small instrument that looks like a cross between a kanoun and a mandolin with a handcrank on one end. The musician cranks with one hand, plays with the other and gets something that sounds like a harpsichord.
I never tip thes guys, although to be fair usually because I don't carry much cash. But the spare change went into his cap!