Some Excel functions that I use often

1. LOOKUP(lookup_value,lookup_vector,result_vector)
   Lookup_value is a value that LOOKUP searches for in the first vector. Lookup_value can be a number, text, a logical value, or a name or reference that refers to a value.
   Lookup_vector is a range that contains only one row or one column. The values in lookup_vector can be text, numbers, or logical values.
2. VLOOKUP(lookup_value,table_array,col_index_num,range_lookup)
   Lookup_value is the value to be found in the first column of the array. Lookup_value can be a value, a reference, or a text string.
   Table_array is the table of information in which data is looked up. Use a reference to a range or a range name, such as Database or List.
   If range_lookup is TRUE, the values in the first column of table_array must be placed in ascending order: ..., -2, -1, 0, 1, 2, ..., A-Z, FALSE, TRUE; otherwise VLOOKUP may not give the correct value. If range_lookup is FALSE, table_array does not need to be sorted.
   You can put the values in ascending order by choosing the Sort command from the Data menu and selecting Ascending.
   The values in the first column of table_array can be text, numbers, or logical values.
   Col_index_num is the column number in table_array from which the matching value must be returned. A col_index_num of 1 returns the value in the first column in table_array; a col_index_num of 2 returns the value in the second column in table_array, and so on. If col_index_num is less than 1, VLOOKUP returns the #VALUE! error value; if col_index_num is greater than the number of columns in table_array, VLOOKUP returns the #REF! error value.
   Range_lookup is a logical value that specifies whether you want VLOOKUP to find an exact match or an approximate match. If TRUE or omitted, an approximate match is returned. In other words, if an exact match is not found, the next largest value that is less than lookup_value is returned. If FALSE, VLOOKUP will find an exact match. If one is not found, the error value #N/A is returned.
   Better to define several cells with names like "table_array" (say, "Check!A1:D10") and "col_index" (say, "3"). After these values are defined properly, the following command can be used:
   VLOOKUP(lookup_value,INDIRECT(table_array),col_index_num,0)
3. COUNTIF(range,criteria)
   Range is the range of cells from which you want to count cells.
   Criteria is the criteria in the form of a number, expression, or text that defines which cells will be counted. For example, criteria can be expressed as 32, "32", ">32", "apples".
4. COUNTIFS(criteria_range1, criteria1, [criteria_range2, criteria2].)
5. SUMIF(range, criteria, [sum_range])
6. SUMIFS(sum_range, criteria_range1, criteria1, [criteria_range2, criteria2], ...)
7. CONCATENATE (text1,text2,...)
   Text1, text2, ... are 1 to 30 text items to be joined into a single text item. The text items can be text strings, numbers, or single-cell references.
8. MATCH(lookup_value, lookup_array, [match_type])
9. INDEX(array, row_num, [column_num])
10. TEXT(value,format_text):
    Value is a numeric value, a formula that evaluates to a numeric value, or a reference to a cell containing a numeric value.
    Format_text is a number format in text form from in the Category box on the Number tab in the Format Cells dialog box.
11. SMALL(range,k)
    Returns the k-th smallest value of the range.
12. LARGE(range,k)
    Returns the k-th largest value of the range.
13. Add a vertical line to a column or line chart: Error Bar Method
14. Lock or unlock specific areas of a protected worksheet