Ultimately, it depends on your supervisor and what are their expectations, so the best advice I have for you is to communicate with them and ask exactly that. Setting an honest and open communication channel with your supervisor is key for succeeding on your doctoral degree. Remember that through a PhD you slowly transition from student into an independent researcher, you should learn how to build and maintain a health professional relation with other researchers - your supervisor is your first collaborator.
Said that, I can share with you my personal experience as someone that finished a PhD in Physics 3 years ago and changed fields completely in the first postdoc in Europe (changing fields in a postdoc is similar to doing a second PhD without a thesis). However, beware that my experience is from Southern Europe and Scandinavia, not UK.
The first meeting
The first meeting between two researchers is usually very exciting. It is likely that your supervisor will tell everything about their projects and all the interesting research that motivates them. They will try to understand what motivates you as well and how you can fit in the research group, sometimes you have the opportunity to collaborate in secondary projects if you are interested. It is possible that they take this opportunity to introduce you to the research group and other colleagues. In my department it is common that the supervisor takes the advisee into a tour in the building, knocking on other colleagues doors and introducing the new student to everyone. When I started both my PhD and postdoc I already had a project with a Gantt chart with milestones, you can discuss with your supervisor and define a timeline for your first year.
Expectations
To start with, familiarise yourself with the PhD program's structure and typical timelines, UK universities often send you a welcome package full of information that you can consult. In my circle, professors do not expected a lot from new international PhD students and postdocs during the first months. You are moving to a new country and you need to figure out many things: immigration bureaucracy, opening a bank account, finding a new home, getting your university credentials, start learning a new language, make friends, etc. Your first year will be dedicated to learn a lot, you will take classes, workshops and you will read many papers to understand the field. In my experience, the literature review takes more than 1 month. At the beginning you read intensively as your main task to catch up with all the important developments in your field and then you start reading parallel with other tasks to keep up with the state of the art. In general you are not required to attend lectures (check at your university), but it is often recommended if they are useful for your research - you can ask your supervisor if they recommend you to attend any course. In parallel to all the scientific learning, you will also start to get familiar with the culture of your new home.
The end of the first year
In general, at the end of the first year you are usually required to submit a report/project proposal, which contains a literature review, objectives, methodology and preliminary results. This document will be useful when writing your actual thesis, but it is natural that many things that you planned in the first year will change. After this you transit from PhD student to PhD candidate, you start feeling more like a researcher and less as student. Of course, this may vary depending on the university, even inside the UK there are some heterogeneity.
This is only my personal experience, but I hope it can be somewhat helpful for others in your situation.
