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Understanding how to align decimal points is vital when performing addition with decimals. Imagine the decimal point as a crucial reference line; every number's place value must be correctly aligned with this line to ensure an accurate sum. For example, when adding 21.36 and 4.573, aligning the decimal points like this:

21.36
+4.573

is essential for maintaining the correct value of each digit. Without this alignment, the individual place values (tenths, hundredths, thousandths) would not align, which could lead to significant errors in calculation. Always remember that the purpose of aligning decimal points is to make sure that digits with the same place value are in the same column before you proceed to addition.

Once decimal points are aligned, the next step is column addition, process akin to stacking blocks with precision. Starting from the rightmost digit, or the least significant place value, add the numbers in each column. Here’s how you tackle it:

• Write down the numbers with the decimal points aligned.
• Begin adding from the column farthest to the right (in our case, the thousandths).
• If a digit is absent, it's equivalent to zero.

In the given problem, we add like this:

Adding the Thousandths

3 (from 4.573) adds with 0 (absent in 21.36) to get 3.

Adding the Hundredths

7 (from 4.573) adds with 6 (from 21.36) to get 13; write down 3 and carry over 1.

Adding the Tenths

5 (from 4.573) adds with 1 (from 21.36) and the carried over 1 to get 7.
Continue this process, moving left and remember to include the carry-over in each addition. When you finish adding the decimal portion, proceed to the whole numbers and add any remaining carry-over. Be meticulous in keeping your work neat, as jumbled digits can lead to mistakes.

Arithmetic operations like addition follow specific rules and methods to ensure accurate results. With decimals, it’s important to handle the decimal point correctly and to perform addition from right to left. Here's a breakdown of the process using our example:

• Start with the smallest place value (thousandths).
• Carry any value over ten to the next left column (tenths, then hundredths, and so on).
• Place the decimal point directly below the others in the result.

Such structured arithmetic operations help prevent errors and confusion. When the operation is completed, you should review your work to confirm the decimal point is correctly placed and that all carried numbers were accounted for. In our case, adding 21.36 to 4.573 following these rules correctly, you should end up with a sum of 25.933.