Every digit has an address.
A digit's column tells us its value. The digit 6 can mean 6 hundreds, 6 tens, 6 ones or 6 tenths.
Read across the chart
Look at 36.4. Each step left is 10 times the value. Each step right is one tenth of the value.
See exactly what changes when you multiply or divide whole numbers and decimals by 10, 100 or 1,000. Build the idea, try it safely, then show what you know.