A new chain will stretch from the stress put on it, to begin with it will stretch more than usual so you need to keep an eye on it. It's a simple job to do, YouTube is your best bet all bikes are pretty much the same so you don't need to look for a specific one to your bike. Just make sure once you've adjusted it that you sit on the bike and check it again (or get someone to help) as you'll add extra tension onto the chain with your weight. You should be checking your chain before every ride, I used to just lift it with my boot as I knew roughy how much it should move from experience, again a visual inspection for lube should be done as well if it looks dry get some spray on it and keep it topped up. Good luck