Imagine that we have a separate Google spreadsheet, and we need to get the B2 cell value to cell D5 on your current sheet.
function copyValueandPaste()
{
var source = SpreadsheetApp.openById('spread sheet id is here'); //Separate spreadsheet book
var sourcesheet = source.getSheetByName('Sheet1'); //Sheet tab with source data
var sourceCellValue = sourcesheet.getRange('B2').getValue(); // get B2 cell value
var thisBook = SpreadsheetApp.getActive(); // Active spreadsheet book
var thisSheet = thisBook.getSheetByName('Sheet1'); // Target sheet
thisSheet.getRange('D5').setValue(sourceCellValue); //Set value to target sheet D5 cell
}
You can find spreadsheet id from your URL.