Two qubits can be prepared as a pair in a shared state. After that, asking for the state of just one qubit is not enough to describe the whole system. Each qubit individually looks random (50/50), but when you compare the measurement results of both qubits, you find they are always perfectly correlated: both 0 or both 1, never one of each. This particular shared state is called a Bell state.

A sentence has meaning as a whole, not as isolated letters. Entanglement is similar: the pair of qubits carries structure that the separate parts do not reveal by themselves. You need to look at both qubits together to see the pattern.

An entangled state cannot be written as a product of individual qubit states $|{\psi }_A⟩\otimes |{\psi }_B⟩$. The Bell state $\frac{|00⟩+|11⟩}{\sqrt{2}}$ is the simplest example: each qubit alone gives completely random results in any measurement basis, but the joint outcomes follow strict correlations. If you measure both in the same basis, the results always match.