My first OHS was emergency with no warning so I had no time to learn about anything. They gave me the spirometer after I left CICU (about day 4) and I had trouble with it at first but kept getting better. Do the best you can as it does help but it definitely is not something for you to worry about in advance.
My second OHS at same hospital, I knew what to expect and sure enough, as soon as I was moved to step down, they gave me a newer model spirometer. One of my nurses said to me that taking deep breaths frequently, as deep as you can, will accomplish the same thing.
It is important to take the deepest breaths you can and if it causes coughing, that will get phelgm out of your lungs which is a very good thing.