I would suggest that, as the other answers say, you should talk to your advisor about this. First off, they will be happy to explain the process to you. In fact, I'd go so far as to take a guess that your advisor will have potentially published in this conference before (you could check their past publications to see if this is the case). Was your advisor aware that you had submitted to the conference? (I will presume so, as in my experience, UK PhD students typically show their papers to their advisors prior to submission). If not, it might be helpful to do so in future, as it allows them to anticipate the potential need for conference funding in advance.
I know that my first publication was at a conference which my advisor had previously presented at many times before (as well as having at one point been an organiser). As to if you will give an oral presentation or not, that is highly conference-specific. My first conference presentation was highly unusual, in that I ended up having around 1 hour to give a presentation and field an extended Q&A session (which was very helpful). Don't fret though - this was highly unusual, and I was aware of it in advance. You will more likely either be giving a poster presentation, or a standard-length presentation with a few minutes for questions. I simply give this example to highlight that you really should speak to your advisor, as every conference is different.
Don't feel silly about asking your supervisor, however. I am sure they will be supportive, and happy to explain how this works. They should also be happy to explain how the process of paying for conferences works (since it is hardly an elephant in the room - conference publications are relatively expensive). There might even be a designated fund to pay for student publications.
While certainly not always the case, I had my own budget for conference travel and registration fees, and was able to simply use this to pay for conferences and travel. For my first conference, I spent roughly the same as you are talking about spending, so that's not wholly unreasonable. Conferences can be expensive, but the opportunities to network, meet other researchers, and share your work are important, and your advisor should understand this and be able to help you understand what is going on.