Get a Server Object
Get the Server Object a Blueprint uses: the typed nodes a Definition asset adds to the palette, finding the object by Target, by asset or with Only One Instance, the Crowdy Server Object component (Instance Id, Signed-In Player, This Actor, This Actor's Area, Player's Team and From Server Value) with its events and nodes, and getting one without the component, with its status.
Read and follow its variables
Read a Server Object's variables from Blueprint with Get and Get Server State, follow each change with On Changed, show the village beacon's oil in a graph and in a widget with Find By Asset, and the by-name nodes (Get Variables, Get Server Value, Watch Variables and the member nodes) for dynamic cases, and Get Players Online for how many players are in the app's world.
Hear its messages
Hear a Server Object's messages from Blueprint with the typed On Message Received node, announce the shared boss's fall with a BossDefeated message and its payload pins, what a game does with a message that arrives while the values are being read or the connection is closed, and the by-name Watch Message and Stop Watching Message nodes.
Call its functions
Call a Server Function from Blueprint with the typed Call node, with a pin for every input and output and On Success and On Failed, the advanced Code pin for a Game Kit starter's refusal, feed the village beacon from an overlap event, give up on a call sooner with Timeout, measure the round trip with Ping Server Objects, and call by name with Make Inputs, Set Server Value and Call Server Function.
Call a Server Function Library
Call a Server Function Library from Blueprint with the typed Call node that needs no Target and no Instance Id, found under Server Function Libraries in the palette, roll loot from the chest on the north road, what the node reports (outcome, reason, retryable, timeout), why the first call after idle can be slow, and why a library offers no Get, On Changed or On Received nodes.
Pins for every type
The pin each Server Object variable, input and output type gets in Blueprint (bool, integers, floats, strings, enums, structs, containers, optionals and the C++-only types), names a node cannot use, types with no pin, and what the nodes do when the asset changes.