Excel 2013 VLOOKUP Question

I am trying to figure out a formula that will allow me to use a drop down box to choose one of several options in column A. I want the formula in column C to then match the choice in Column A because my calculations will be different in column C based on the column A choice. User input occur in column B with the resulting data being displayed in column C.
I am trying to use a VLOOKUP with a table array on another sheet. But having Excel look at column A and then saying "If column A = XXXXX then go to another sheet and grab this text "XXXXXXX" and put it in column C" seems to be difficult. Or at least it is for me. I can't seem to get it to work properly. I thought that I had it figured out last week but I was only getting it to input one formula. I wasn't getting it to look at the data in column A and THEN go lookup an entirely new table to find the appropriate formula and then deposit that formula into the same row in column C.

We shall need to get your thread title improved, but at the moment, I am not clear about what you are trying to do.

Will you please attach a sample Excel workbook? We are not able to work with or manipulate a picture of one and nobody wants to have to recreate your data from scratch.

1. Make sure that your sample data are REPRESENTATIVE of your real data. The use of unrepresentative data is very frustrating and can lead to long delays in reaching a solution.

2. Make sure that your desired results are also shown (mock up the results manually).

3. Make sure that all confidential data is removed or replaced with dummy data first (e.g. names, addresses, E-mails, etc.).

4. Try to avoid using merged cells as they cause lots of problems.

Unfortunately the attachment icon doesn't work at the moment, so to attach an Excel file you have to do the following: just before posting, scroll down to Go Advanced and then scroll down to Manage Attachments. Now follow the instructions at the top of that screen.

Please pay particular attention to point 2 (above): without an idea of your intended outcomes, it is often very difficult to offer appropriate advice.