Finding the function that you need to do numeric calculations is easy, you will find all the functions in the Number object. For a full list of all the available Number functions: Number functions – PowerQuery M | Microsoft Learn.

let
    varUnitPrice = 12.55,
    varQuantity = 5,
    varLineTotal = varQuantity * varUnitPrice,          // 62.75
    
    varRound = Number.Round(varLineTotal),              // 63
    varRoundDown = Number.RoundDown(varLineTotal),      // 62
    varRoundUp = Number.RoundUp(varLineTotal),          // 63
    varModulo = Number.Mod( varRoundUp,  2),            // 1
in
    varModulo

If you want to convert Text into a Number you use the From() function specifying the Region (Culture) in the second argument to parse the Text. For a full list of all the available Cultures: List of Windows LCID Codes. 

varParse = Number.From("12.34", "en-us"),         // 12.34

Formatting numbers as Text is done using the ToText() function. For an overview of supported formatting codes for Numbers: Custom numeric format strings – .NET | Microsoft Learn

varFormat = Number.ToText(varParse, "€ 0.0")      // € 12.3