Hi, paramveer!
Don't worry about your English, there are a lot of people for whom it isn't their native language -as in my case- and everybody make their best efforts to correctly interpret everything that's posted.
The formula.
=INDEX('salary book'!$A:$Z,MATCH(B2,'salary book'!D:D,0)+21,13)
INDEX is a function whose syntax is "INDEX(matrix, row number[, column number])" and it retrieves the value of matrix for a given row and column (which might be optional so it's into square brackets), being in the example:
matrix: 'salary book'!$A:$Z, columns A-Z of worksheet 'salary book'
row number: MATCH(B2,'salary book'!D:D,0)+21
column number: 13
MATCH is a function whose syntax is "MATCH(value, matrix, type of coincidence)" and it retrieves the relative position on matrix where value is found, being in the example:
value: B2 cell
matrix: 'salary book'!D:D, column D of worksheet 'salary book'
type of coincidence: 0 (exact match, other possible values are 1 for approximate search in ascendent order and -1 for descending order)
So the whole formula does this, it retrieves from the worksheet 'salary book' the cell at the row where it found the B2 value (Tiger, Beer, ..., i.e., row 1, row 23, ...) plus 21, that's to say 22 for Tiger and 44 for Beer, and at the column 13. And what addresses are those of row 22 column 13 and row 44 column 13? M22 and M44, that where your indications for cell D6 of worksheet 'Income Tax'.
Hope it explains how does the formula works.
About your formulas in red that I changed for you in blue, those were for your red ones for which you provided in their comments an exact description of what columns from worksheet 'salary book' you wanted to retrieve. And about your formulas which I left in red that is because you didn't provide an exact method for identifying them (not all of us are from your country, whichever it is, not all of us are accountants nor payroll nor tax experts, ...) so for cell D26 the comment "captain: here also" doesn't give any clue of what to do. Despite of this I tried to find any relation between B26 cell contents "ELSS/NSC/PPF etc." and the header row 4 of 'salary book' and none matched.
That's why -and this is the 3rd time- I told you that your homework was identifying the correct (unprovided) column of 'salary book' that corresponded and then changing the 13 value (for column M) in the sample formula for the correct value for the involved column, repeating this process for each cell in red.
Regards!