Magnetic activity is a ubiquitous feature of stars with convective outer layers, with implications from stellar evolution to planetary atmospheres. Investigating the mechanisms responsible for the observed stellar activity signals from days to billions of years is important in deepening our understanding of the spatial configurations and temporal patterns of stellar dynamos, including that of the Sun. In this paper, we focus on three problems and their possible solutions. We start with direct field measurements and show how they probe the dependence of magnetic flux and its density on stellar properties and activity indicators. Next, we review the current state-of-the-art in physics-based models of photospheric activity patterns and their variation from rotational to activity-cycle timescales. We then outline the current state of understanding in the long-term evolution of stellar dynamos, first by using chromospheric and coronal activity diagnostics, then with model-based implications on magnetic braking, which is the key mechanism by which stars spin down and become inactive as they age. We conclude by discussing possible directions to improve the modeling and analysis of stellar magnetic fields.

磁活动是具有对流外层的恒星的普遍特征，其影响从恒星演化到行星大气层。研究从几天到数十亿年观测到的恒星活动信号的机制对于加深我们对恒星发电机（包括太阳发电机）的空间配置和时间模式的理解非常重要。在本文中，我们重点讨论三个问题及其可能的解决方案。我们从直接现场测量开始，展示它们如何探测磁通量及其密度对恒星特性和活动指标的依赖性。接下来，我们回顾当前最先进的基于物理的光球活动模式模型及其从旋转到活动周期时间尺度的变化。然后，我们概述了目前对恒星发电机长期演化的理解状态，首先使用色球层和日冕活动诊断，然后基于模型对磁制动的影响，磁制动是恒星旋转并变得不活跃的关键机制随着年龄的增长。最后，我们讨论了改进恒星磁场建模和分析的可能方向。