So I am pretty sure I don't know how to do this

Need a little more info. Decals are self adhesive and don't require cement

Now calm down trooper, you don't get to qualify until you get to the range.

So: after your clear gloss coat has dried and your ready to start the decaling process.

1. Cut the decal (one each-decal # 001) you want to apply, from the sheet
2. place it into warm water for a few seconds -thickness and composition of the backing paper will have an effect on the time.
3. As the decal loosens -you may notice the backing paper is uniformly "wet" , carefully remove it from the water(don't let the decal slide off the backing paper).
4. Place the decal side, UP, on a bit of paper towel to wick the big water blobs away.
5. Handling with great care, gently place the backing paper as close to the location on the model, as you can.
6. Gently slide the decal off onto the model (a small soft, wet, brush is good to use) and 
7. put it on the spot you need it to be; sliding it on the wet area of the model.[think skiing on concrete in summer vs snow in winter]. 
8. Taking the torn edge of a paper towel just touch the wet area (not the decal) and wick up the excess water. 
9. Then using the damp paper towel gently/lightly blot the moisture off the decal 
10. Use of decal solvents`-Micro Sol- for instance may be applied to help the decal settle in to the panel lines etc.
11.  Repeat for the rest of the decals on the sheet - always one at a time; unless you like to live on the edge- like doing an Australian repel from a Blackhawk  . .............................................................
12. After all the decals are all dried and settled and all snuggled in, 
13. cover with a clear coat (gloss is the usual)  which will seal the decal from ham-fisted modelers or further weathering.

  This is the quick primmer.  The details found and suggestions offered, you by others need to be taken into account and added to you process as you need.

Alright, AT Ease; you are, dismissed, to return to you modeling.

That post is exactly what I needed! Saved as PDF and sent to the file server so I will never loose it.

Now, how do I go about getting a second set of decals for this 1:35 WWII American Sherman tank?

Here is one spot to get decals,,,,from the people that print decals for themselves and for other companies.

www.microscale.com/.../merchant.mvc

hope this helps

Rex (my brother in law is on Ft Hood)

what make is it? can the manufacturers help. i have had replacement decals from tamiyas uk supplier and from airfix uk too. find a retailer who you can order spares from. look at the kit manufacturers  website, they possibly have your local distributor listed there.

It is a Revell of Germany model and I have already filled out the replacement parts form. But that decal selling site is really tempting!