The execution engine interprets a Plan as a series of statements and blocks, in a top-down manner.
If you're comfortable with programming or scripting, you'll probably already be familiar with how these blocks work. There is a formal specification available if you want to know precisely how the execution engine and plans/OtterScript work.
Blocks provide an easy way to organize your plans, and the sub-tasks those plans are made of. They can be nested as many levels deep as you need. All blocks provide variable scoping (i.e. if you set a variable in that block, it will only be available within that block) as well as log scoping.
Otter's logs were designed to be as easy to navigate and understand as plans. this is where collapsible log scopes come in:
If you give a block a short description, then the plan's execution log will have a scope of the same name. This way, as you nest statements and blocks in your plans, they will have parity in the log.
Because logs may contain sensitive data, such as the arguments to a command line, you can Restrict Users from viewing debug-level logs. This offers an ideal mix between security/compliance and visibility.
When an Asset (template plan or script) is used in a plan, it is run as an operation, and can be treated in the same way (moved within a plan and have custom configurations). It is logged as an operation as well.