Hi, OP -
I am a former admissions tutor. I know the process can seem overwhelming.
The link from @Sadsadworld should be helpful - UCAS are the central admissions organisation for undergraduate admissions in the UK.
Here is a brief summary.
The Open Days people are referring to are large information sessions. The Central Admissions team for each uni will have a big booth and run some talks, and usually various subjects and degree programmes will have their own booths, staffed by Admissions Tutors. There will often be talks in various subject areas as well as the talks by the Central Team.
Sometimes the audience is limited to prospective applicants and a plus one, as otherwise whole families like to attend and crowd out the prospective applicants. Sometimes you need to register for talks ahead of time. All of this should be on the website for the Open Day.
Are you near any universities? Just getting to an Open Day is the first step.
DD will get predicted grades, usually early in the Autumn. These should be used to guide the choice of university and degree programme. I usually think applicants should apply to one degree programme that is a bit of a stretch, if they are really attracted to it, 3 programmes that are a good match for their predicted grades (I will return to this), and one absolute safety programme, with entry requirements 2 grades below their PGs.
In a super competitive field like Economics or Computer Science be aware that for highly ranked programmes, to get an offer of a place you need PGs one or two grades higher than the stated entry requirement.
As DD figures out what universities appeal to her you can line up other Open Days, if she wants. But visiting for an interview, or at an Offer Holder Day, is generally more satisfying. These happen later.
Timeline: Oxford, Cambridge, Medicine
Anything else, MumsNetters?
Applications due in October
Other applications due in January
You will learn the results of your 5 applications through UCAS. It takes variable amounts of time.
Select your Firm and Insurance choices, dropping your other choices, by June
Obviously, check my dates against what UCAS gives for next year!
Then wait for your exam results
I hope this helps. Best wishes