The Junos OS configuration consists of a hierarchy of statements. There are two types of statements:
Container statements, which are branches that can contain other statements (including additional container statements or leaf statements). Container statements at the top of the hierarchy are considered to be the trunk of the hierarchy tree.
Leaf statements (contained by container statements), which do not contain other statements.
The container and leaf statements form the configuration hierarchy. Each statement at the top level of the configuration hierarchy resides at the trunk of a hierarchy tree. These top-level statements are container statements, containing other statements that form the tree branches. The leaf statements are the leaves of the hierarchy tree. An individual hierarchy of statements, which starts at the trunk of the hierarchy tree, is called a statement path.
Ex:
interfaces {
interface-name {
disable;
description <text>;
encapsulation <type>;
hold-time up <milliseconds> down <milliseconds>;
no-keepalives;
keepalives interval down-count up-count;
serial-options {
clock-rate <rate>;
}
speed (10m | 100m);
unit <logical-unit-number> {
bandwidth <rate>;
description <text>;
disable;
family family {
address <address>;
}
}
}
Please check this for complete guide on Configuration Statements Hierarchy
You may also check this for Juniper Network Simulator with Designer
Also check this for Juniper available practice labs