The loops represent convection and the zigzag arrows represent radiative transfer.
Note, the cartoon is slightly wrong in that stars with stellar mass ⪅ 1.2 M_☉ have outer convection zones, those with stellar mass in the range ∼ 1.2--1.3 M_☉ have NO convection zone, and those with stellar mass ⪆ 1.3 M_☉ have inner convection zones. Note also, relatively few stars have NO convection zone, and so one often says nearly all stars have convection zones.