This is not supposed to be an exhaustive live of excel formulas for that I would suggest visiting https://exceljet.net/formulas but rather key formulae/functions that could prove useful for your work in Planning and Insight.
Other notable sources of information on excel.
Sum values between two given dates of a data range, to average numbers between two dates also can be solved by using some formulas
A quick and easy way to count between dates is by using the COUNTIFS formula, create formula-based filters.
As it sounds, but an explanation of how to use this.
Using sumproduct and countif to gain the number of unique values within a range.
The INDEX function can be used alone, but nesting the MATCH function inside it creates an advanced lookup.