Originally Posted by well biked
It sounds like a worn out chain to me, or a new chain being used on worn out freewheel cogs. Either way, it sounds like the chain isn't meshing properly with the teeth on at least some of the rear cogs-
Clip from OP: "I just bought a new bike..."
So not likely worn chain. More likely stretched shift cable/settling of ferrules typical of new bike after short usage.