Node is the point of connection between elements. Elements connected to the same nodes have the same voltage.
Branch: is the connection between two nodes. The elements in the same branch carry the same current.
Loop is the closed loops in the circuit diagram.
A network with b branches, n nodes, and l independent loops will satisfy the fundamental theorem of network topology:
Series Connection: Two or more elements are in series if they are connected sequentially and consequently carry the same current.
Parallel Connection: Two or more elements are in parallel if they are connected to the same two nodes and consequently have the same voltage across them.
Algebraic sum of currents entering a closed loop (or a node) is zero.
Don't forget to use plus sign for current entering into node and negative sign for currents leaving the node if just the magnitudes are given.
Algebraic sum of all voltages around a closed path (or loop) is zero.
If you meet with negative terminal of an element first, write that voltage as negative to the equation.