Copy the sake file to either your project's .ddev/commands/web folder. Or, for global usage, copy it to {YOUR_HOME_FOLDER}/.ddev/commands/web
Sake is the Silverstripe Make command, to run development tools.
Use it as sake in your project:
ddev sake dev/tasks for tasks
ddev sake dev/build to build the database
etc.
For the full list of features of Silverstripe CLI, see the Silverstripe (developer) documentation.