In grade 4, students are not required to use the standard algorithm to add or subtract decimals. That is, they do not have to vertically add them by lining up the decimals.
Since they just deal with tenths in this grade, this means the key operational sense understanding is to fully comprehend that it takes ten tenths to make a whole.
This is one of the essential understandings of decimals: unitizing. This just means that in our place value system, you need ten smaller pieces to make one larger unit to the left, or each larger unit is made of 10 smaller units.