Your question is very vague.
There are several examples in the example finder on how to calculate FFTs. Have you tried to look at them?
There are also several examples on how to read data from excel and on spreadsheets in general. The example finder can be opened by clicking Help>>Find Examples.
If this didn't help, I suggest you post some more details about what you're trying to achieve.
To learn more about LV, I suggest you try searching this site and google for LabVIEW tutorials. Here and here are a couple you can start with. You can also contact your local NI office and join one of their courses.
In addition, I suggest you read the LabVIEW style guide and the LabVIEW user manual.
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