The SUM function in Excel is a workhorse for adding up values. Here's how to use it:

Basic Syntax:

```excel
=SUM(range)
```

Breakdown:

- `=` : This signifies the beginning of a formula in Excel.
- `SUM` : This is the function itself, indicating you want to calculate a sum.
- `(range)` : This is where you specify the cells you want to add up. You can enter the cell range directly (e.g., A1:A10) or select the range with your mouse.

Examples:

1. Sum a range of numbers:

```excel
=SUM(A1:A10) // Adds values from cells A1 to A10 (inclusive).
```

2. Sum individual cells:

```excel
=SUM(A1, B2, C3) // Adds the values in cells A1, B2, and C3.
```

Additional Notes:

- You can mix and match cell references and numbers within the range argument.
- The SUM function can handle blank cells and text entries containing numbers (e.g., "123") and will include their numerical value in the sum.
- For cells containing errors (e.g., #VALUE!), the SUM function will ignore them by default.

Tips:

- Use AutoSum: If you need to sum a simple range of numbers, you can use the AutoSum button on the Home tab. Excel will automatically suggest the appropriate range based on your cursor location.
- SUM with logical functions: You can combine SUM with other functions like IF or COUNTIF for more complex calculations.

By mastering the SUM function, you can efficiently perform various calculations in your Excel spreadsheets.