Define the initial state of your two-qubit system. This is a 4-dimensional complex vector:
$|\psi\rangle = \alpha_{00}|00\rangle + \alpha_{01}|01\rangle + \alpha_{10}|10\rangle + \alpha_{11}|11\rangle$
Remember that the sum of the squares of the magnitudes of all amplitudes must be 1: $|\alpha_{00}|^2 + |\alpha_{01}|^2 + |\alpha_{10}|^2 + |\alpha_{11}|^2 = 1$.
A common starting point for entanglement is the state $|+\rangle|0\rangle = \frac{1}{\sqrt{2}}(|00\rangle + |10\rangle)$, which is set as the default.
The **CNOT (Controlled-NOT) gate** flips the target qubit if the control qubit is $|1\rangle$. If the control is $|0\rangle$, the target remains unchanged.
This gate is essential for creating **entanglement**.
The **complex amplitudes** show the full quantum state, including phase information crucial for entanglement.
The **measurement probabilities** tell you the likelihood of observing each classical outcome when you measure the qubits.