I was going through a Quantum Computation lecture series on YouTube given by Umesh Vazirani. There in Lecture 6.3 he talks about creating a Bell state using a Hadamard and CNOT gate. He seems to be using |0⟩ and |1⟩. Is he talking about measuring a qubit in 0-1 basis and then using the qubits that gave 0 as a result for the |0⟩. Here is an image for reference.