  Developers frequently move into new teams or environments across software
companies. Their onboarding experience is correlated with productivity, job
satisfaction, and other short-term and long-term outcomes. The majority of the
onboarding process comprises engineering tasks such as fixing bugs or
implementing small features. Nevertheless, we do not have a systematic view of
how tasks influence onboarding. In this paper, we present a case study of
Microsoft, where we interviewed 32 developers moving into a new team and 15
engineering managers onboarding a new developer into their team -- to
understand and characterize developers' onboarding experience and expectations
in relation to the tasks performed by them while onboarding. We present how
tasks interact with new developers through three representative themes:
learning, confidence building, and socialization. We also discuss three
onboarding strategies as inferred from the interviews that managers commonly
use unknowingly, and discuss their pros and cons and offer situational
recommendations. Furthermore, we triangulate our interview findings with a
developer survey ($N=189$) and a manager survey ($N=37$) and find that survey
results suggest that our findings are representative and our recommendations
are actionable. Practitioners could use our findings to improve their
onboarding processes, while researchers could find new research directions from
this study to advance the understanding of developer onboarding. Our research
instruments and anonymous data are available at
\url{https://zenodo.org/record/4455937#.YCOQCs_0lFd}
