It is difficult to give advice without specific examples... Pay close attention to the syntax of the functions... For example:
VLOOKUP(lookup_value, table_array, col_index_number, [range_lookup])
lookup_value is always the value it is trying to find. It must be in the first column of the table_array.
table_array is the set of data you want to look through.
col_index_number is the number of the column in the table_array you want to grab the result from. If you say 1, it will return the lookup_value if it finds it. 2 will be the cell directly to the right of the lookup_value.
[range_lookup] just asks whether the list is sorted. If it is, say TRUE and the VLOOKUP will be slightly faster for long lists. If you are unsure or don't want to worry about it, say FALSE.
I also recommend wrapping all your VLOOKUP and MATCH formulas in IFERROR statements. IFERROR(value, value_if_error) is the syntax.
value is where you put the VLOOKUP function.
value_if_error is where you can put "No Match" or something similar, so that you won't get #VALUE errors in your spreadsheet.
Pay attention to the color-coding that Excel automatically does to tell where you are inside the formulas. It'll help you get out of a jam.
Good luck!