These videos all come from the Khan Academy. in all vertical methods of addition and subtraction it is important to line up correctly, this is explained in the videos and how to do it with decimals. They go over how crucial it is to line up the numbers so you add or subtract units to units, tenths to tenths, hundredths to hundredths and thousandths to thousandths.
Once you’ve seen them, set a few for yourself to see how you get on.
Caution: where we would use the word, the video uses the word regroup. It does the same thing so don’t worry! Importantly you will see why we need to put place holders in to help us.