It’s really not as scary as you think - you can do all sorts of things to make a fancy roast but a simple one is really straightfoward.
The time for cooking the chicken will depend on the weight of the chicken you have. There will be instructions on the label - it may say something like “Cook for x minutes per kilogram”. If it does, the weight will also be on the wrapper so you can calculate it.
Turn on the oven to heat it up. Stick the chicken in a baking tray (preferably a deep one). I tend to rub a bit of olive oil on the skin to make it crispy (just a light drizzle over the bird then rub it in). Then plenty of salt and pepper. Then simply cook for as long as it says on the wrapper. For extra crispy skin you can take it out every so often, spoon the juices from the roasting tin over the skin a few times during cooking.
Roast potatoes are easy when you know how. They need about 45-60 minutes in the oven so calculate when they need to go in the oven based on the chicken. 15 mins before that peel the potatoes (you don’t have to) then cut into halves or quarters. Put in a pan of cold water with a bit of salt. Bring to the boil with a lid on (if you have one), then turn it down to simmering for about 10 mins. If you stick a fork in potatoes they should be slightly softer but not falling apart (although if they are falling apart it’s not the end of the world, it’s happened to everyone).
Put another baking tray with a couple of tablespoons of oil in the oven to heat up. Drain the potatoes in a colander and let them sit there for a minute.
For the best potatoes, chuck them back in the saucepan. Add salt and pepper and a tablespoon of flour if you have it (not essential), put the lid back on and shake vigorously so the potatoes get a bit bashed up. Then carefully put them into the hot tray from the oven (use a spoon and do one at a time so you don’t get burnt)
Or you can skip all that - drain them then put them straight into the hot baking tray (again add salt and pepper and be careful not to get burnt)
Then stick them in the oven, and turn halfway through cooking. That’s it.
If either the chicken or the roast potatoes are done before the other, just take them out and cover with foil to keep them warm - if they’re out for a long time you can always pop them back in at the end for five minutes.
Make stuffing separately if you want it.
For gravy I’d use instant if I were you. To make real gravy, you stick the pan you cooked the chicken in on the Hob, add a tablespoon of plain flour to the juices and stir until it all comes together in a sort of paste and cook that for a few minutes, then add boiling water (bonus points if you add chicken stock or chicken stock cubes).
Depends what other veg you’re cooking but most can be boiled or steamed - test with a fork to see if it’s done.