If the repository is level 2 compliant (see 4.2 Compliance Levels) then, having acquired a session, the client can write to the repository by adding or removing nodes and properties or changing the values of properties.
For example, the client can retrieve a node, add a child node to it and add a property to that child node:
// Retrieve a node
Node myNode = (Node) mySession.getItem("/a/e");
// Add a child node
Node newNode = myNode.addNode("n");
// Add a property
newNode.setProperty("x", "Hello");
// Persist the changes
mySession.save();
The node myNode has the path /a/e, so the new node will have path /a/e/n and the new property will have the path /a/e/n/x and the string value “Hello”.