A made-up poll asks 900 parents, chosen at random, whether they want school uniforms…

Step 1. Standard error. $\sqrt{\dfrac{0.64 \times 0.36}{900}} = \dfrac{0.48}{30} = 0.016$.

Step 2. Margin. $1.96 \times 0.016 = 0.03136 \approx 0.0314$.

Step 3. Interval. $0.64 - 0.03136 \approx 0.609$ and $0.64 + 0.03136 \approx 0.671$.

What it means. We are $95\%$ confident that between about $61\%$ and $67\%$ of all the parents want uniforms.