Drive chain tensioner

I just bought this car and it needs a new tensioner. I've only gotten as far as getting the valve cover off. Can't seem to remove the drive chain cover due to something attached to the back of it. I don't know what this is and if you even need to remove it to get the cover off. Also, are there any important things I need to know doing this job as this is my first time working with this type vehicle. I'm a bit nervous that it's going to get all dried out inside. And that it's not going to run once I'm done. Please help with some experienced advice.