Portfolio advice -
My general portfolio advice for anyone applying to arts courses is include a combination of examples of iteration/development/design work (often the kind of thing you might do in school), some drawings from life (e.g. still life, figure drawing, technical drawing) and imaginative work (work that demonstrates combining ideas imaginatively). Some places might request a variety of mediums, and this is often course-dependent - I would expect in your case they would at least expect to see some painting and some drawing, which it sounds like you have. Always read the unique portfolio guidance for the courses you are applying to, as they may suggest other things they'd like to see i.e. they might value seeing large-scale works, or have some stipulation about including X thing, or whatever else. I would also imagine for a Fine Art course they'd like to see evidence of your understanding of the art world i.e. work that references other artists, or annotations on your work that reference this. For Craft Design they might want to see examples of textiles work, modelmaking, pottery, or other 3D art forms.
You may also benefit from looking at examples of successful applicant portfolios to the courses you are applying to on Youtube.
Interviews -
If you're invited to an in-person interview, you will need to bring you work presented in some way. This might be in formatted sheets that are printed and showcased in a binder, but it also may include bringing sketchbooks. They will usually give you an idea of what they want you to bring when you're invited to intevriew, but if you are studying on art course now, they will also be able to provide advice on what to bring. You might want to dress smart but there's no reason to be overly formal.
When you get there, you will usually be in a room full of other applicants as they call people up one by one for interview. Take the opportunity to chat to other people, as often you might be applying to several of the same universities, and they are often nervous too!
You will be expected to present your work in interview - whatever you do, don't just stand there in silence and turn pages! You need to be able to talk about each of your pieces, be able to explain your decision making for any artistic decisions you made, why you included each piece, and know some information about the university and the course you are applying to, in case they ask you any questions about why you have chosen this specific uni/this specific course. I can recommend just trying to present your work before you have to do it in interview - talk through your work to a friend or family member before you go. It will also help you judge if you're going too quickly/too slowly!
You might get an opportunity after/before your interview to tour campus/accommodation/etc if you hadn't previously had the opportunity at an open day.
If you have an interview online (as these become more common) the same principles apply, but you'll probably be talking through an online submission as opposed to a physical display. It may be harder to judge the pace you're going at as they may be the one scrolling through your work and not you. (dependent on if you were asked to submit things in advance, but this is pretty common) You still need to be able to talk through your work in much the same way. You might have less preparation you need to do in advance.
Best of luck to you!