My suggestion even though you are not well versed with the lookup or vlookup functions you should learn them they really are as easy as IF formulas. The tool tips when creating a formula walk you through creating a vlookup but just so you have an idea.

=vlookup( < the formula which we will write in D1
=vlookup(The reference cell that the vlookup looks for in this example we will say A1
=vlookup(A1,Now you need to tell the formula what table to look in we will say b1:c12 in cell B1 type 1 B2 2 B3 3 etc., then in cell C1 type Jan then in C2 type Feb, C3 Mar etc.
=vlookup(A1,B1:C12 Now you tell the formula what column of the table to look in b1:c12 only has 2 columns but we want to look into the 2nd one so we would write 2
=vlookup(A1,B1:C12,2 Last part do you want the formula to find an exact match only or get something closest to it. 0 is an exact match and 1 is find the next closest. So it you put in 1.7 in A1 the vlookup will give you the value of 2 which will say Feb in our example.
=vlookup(A1,B1:C12,2,0)

There it is let me know if you have any questions or if you want me to try and correct your formula to Vlookup.

Thanks