It's a scary way to start an already scary job, but it's manageable.
I would strongly recommend speaking to as many FY1s as possible during your shadowing period to find out where you're expected to be and what your responsibilities are as it works differently in every hospital, and differently in surgery vs medicine.
For example, you need to find out whether you'll be clerking new admissions or covering the wards, or both. You need to find out where handover takes place (usually SAU/MAU doctors office). Get one of those cards with bleep numbers on it and make sure you know how to bleep. When it doubt, go through switchboard. Also, it will probably be your job to make a list of new admissions at the end of the night for the ward round. Your department may already have old lists saved on the computer that you can use as a template (just basics like demographics, bed number, presenting complaint. Surgery seems to like lists with blood results and imaging which is a ballache).
My second tip would be to make a jobs list and be organised. If you're covering the wards, arrange it by location so you can do things as you're in that place. If you're clerking, make a list with tickboxes for bloods, imaging, regular Rx, management, VTE assessment and fill them in as you go along.
Third, when in doubt, do an A to E assessment before anything else. And if you feel out of your depth or you get more than one sick patient at a time, call for help. Do the basics: IV access, bloods, gasses, ECG, CXR, fluids. Use the intranet for local policies and antibiotic prescribing.
Finally, look after yourself. Nobody will tell you to have a break, but there will be plenty of people who will ask you for one last "five minute" job. They don't care that you haven't had a drink in 7 hours, they just want you to prescribe whatever ********.
It will be a good year and a **** year but you will grow as a doctor. Stick together with the other FY1s and engage with mess events. Blowing off steam with your colleagues will keep you sane.