What is Lando? From the Lando documentation:
It's a free, open source, cross-platform, local development environment and DevOps tool built on Docker container technology and developed by Tandem. Designed to work with most major languages, frameworks and services, Lando provides an easy way for developers of all skill levels to specify simple or complex requirements for their projects, and then quickly get to work on them.
In simpler terms, it is a container system built on Docker that runs on Windows, MacOS, and Linux, letting you spin up development websites with a minimum technical hassles. It is just one of many ways to easily set up a Drupal 10 development site for either building a complete new website, doing module development work, or testing third-party modules in a safe "sandbox" environment.