I remember being stressed about this beforehand, but it's really not as difficult/intimidating as it might sound. Get the vibes from your team on your first day, you'll see who's approachable and who's not. For me, it was a quiet office day with most people working from home but my supervisor briefly took me around the floor and introduced me to the 5 or so people who were there.
Halfway through the day I day I was close to finishing my first (and only task). Went to the kitchen to make a coffee and had a quick chat with one of the associates about nothing in particular. Before heading back to my desk I mentioned I was free to help out with anything and she goes "oh actually I do have something, I'll email it over this afternoon and we can go chat about it." Another time I was chatting with my supervisor about a task and mentioned I had capacity, she asked around for me, and two different people came back with tasks for me.
But similar to my coffee chat comment, don't feel like you have to do this if you have enough work. It's so easy to get overwhelmed, and nobody expects you to seek out work if you have enough. I know for a fact that the other vac schemer in my department never sought out work. He spent the whole scheme on maybe 3 massive tasks for his supervisor and nothing else, and managed to get the TC.
Like with everything on these schemes, it's a 'go with the flow.' I know some people have sent a team-wide email or openly announced at a breakfast networking event that they are happy to help with anything, but to me, that felt uncouth and over the top. My team was so laid back and friendly, so I took that approach too.