The H, or Hadamard, gate rotates the states and to and , respectively. It is useful for making superpositions. If you have a universal gate set on a classical computer and add the Hadamard gate, it becomes a universal gate set on a quantum computer.
For more information about the H gate, see HGate in the Qiskit Circuit Library.
Composer reference
OpenQASM reference
Q-sphere
Note about q-sphere representations
h q[0];
The q-sphere representation shows the state after the gate operates on the initial equal superposition state where is the number of qubits needed to support the gate.
