PQ provided some pretty spot on advice there. I'd just clarify the foundation route isn't uncommon - often students don't have suitable portfolios out of A-levels/etc, and the foundation is more or less designed around building up a suitable portfolio.
Sometimes you can go directly into a specific area of focus but usually you spend the first term exploring different areas of the creative arts, then specialise in one, doing various work based on briefs set by the tutors, then finish with a major self led project. It's a useful metric for universities as they know having completed it, in theory, you will have a broad base of creative skills, as well as specific design/other ability in your chosen area, and the ability to both respond to external briefs and to develop self-generated work.
It's particularly useful if you're interested in areas less commonly emphasized in school - like animation, illustration, spatial design etc, although still beneficial for Fine Artists or similar.
Some Foundation Courses are designed to lead internally to one of the providers degrees (while retaining the option to apply to/continue on to others) such as the UAL foundations. This isn't universal and is mainly a perk, but students from other foundations gain places on such courses regardless (and it's usually less possible for students to pursue such a foundation if they don't live in or around London, as the foundation course is an FE course as stated - so you are not eligible for SFE funding, namely the maintenance loan. It is free for students who are under the age of 19 at the start of the course though, so if you think it's a possibility I would suggest applying even if you're not sure as if you wait a year you may have to pay fees).