The following are 6 good formula reference sites for SharePoint – PowerApps – Power Automate:
Introduction to SharePoint formulas and functions:
Examples of common formulas in lists:
Formula reference for Power Apps:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/formula-reference
And, Or, and Not functions in Power Apps:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-logicals
Date and Time functions in Power Apps:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-date-time
Use expressions in conditions to check multiple values:
https://docs.microsoft.com/en-us/power-automate/use-expressions-in-conditions