The good news is that OsCommerce is fairly flexible in how do define options.  The bad news is that it takes a lot of work to create the foundation.

 

Here are a few things you need to think about before entering options.

1. Option types.  You need to create an option type like size, color, material, or confirmation.  Pick the name well because it shows on your catalog next to the pull-down arrow.  Also think forward.  On a shoe website we had one type for size and another for width because that's the obvious way to do it.  When we put them into a shoe, we discovered that a customer could order a combination that didn't exist.  So after entering all the values for size and width, we had to start over.
   
2. Option values.  These are the choices the customer will see.   You'll enter one for each value.  This step is very laborious so plan ahead.   In the shoe example, we have 8M, 8W, 8WW, 8B, 8D, 8E, 8EE, 8EEE.  Consider that shoes come from 4 and go to 14 or more, that's a lot of entering.  You don't want to do it more than once.
3. Sequence of entry.  You can enter the options values in any order you want.  The system doesn't care and it keeps them in the order of entry.  Having said that, I strongly recommend you enter them in groups that make sense to you.  This is because you will eventually need to edit one of them and finding them can be a real pain.  If they are in radom order, you'll need to flip through countless pages looking for the option value.  If they're in groups, you can flip more easily.  If you have products without many options, don't worry about.
4. How to create a decision option.  For this you just create an option type that is the decision.  "Do you want the free gift?" is an example.   The options values will be "yes" and "no".  You'll see later how to add options attributes to a product.

Now the work part:  Adding option type is first.  You can't add values until you have an option.

1. Log in and click on "Catalog".
2. Click on "products attributes" in the navigation on the left.
3.  The first table is labeled "product options" 
   
4. At the bottom of the table is an entry box.  Enter the option name and click "insert"
5. Repeat until all option types are entered.   They should show up in the table.

Adding Option Values

1. If you're not already there, login and click "product attributes"
   
2. We'll be working with the second table, "Option Values".
3. At the bottom is another place for entry.
4. Select the Option name from the pull-down.
5. Enter the option value.
6. Click "insert"
7. Repeat until all option values are entered. 
   
8. If you're doing maintenance, be sure to check to make sure you don't already have that option value.  The easiest way to check is use the table at the bottom.  There is a pull down for option values.  It should be the third from the left.  First is product name, second is option type and third is option value.