You can insert numbers directly into the function by using commas between them.
You can also simply refer to a range for calculating the sum of the numbers. And if there is text, logical values or empty cells in those cells it will ignore them.
If there is an error value in a cell which you are referring, it will #N/A in the result.
If you have numeric values which are formatted as text it will ignore them. It's recommended to convert them into numbers before using SUM.