In modern datacenters and clouds, Resource Disaggregation has been adopted as a way of offering scalability and efficient resource utilization for large-scale applications. Provisioning CPU, memory, and storage resources independently for distributed data-intensive applications is a great enabler but it also brings challenges, especially in the form of networking and processing overhead. To reduce this overhead and to make disaggregation-related tasks significantly more efficient, cloud providers are offloading these to the network, i.e., to Smart Network Interface Cards (SmartNICs) and Smart Switches. Beyond this specific use-case, the presence of such programmable hardware in commercial clouds creates future opportunities for offloading application-level operations, e.g., parts of SQL queries or ML pipelines. To map out this exciting space, in this tutorial we take a detailed look at SmartNICs, explaining how they work, giving examples of what they are good for, and highlighting how they can best be utilized to make future data-intensive and distributed systems more efficient.