Find a degree
Applying for an undergraduate degree in microbiology is much like applying for a degree in any science. For most courses you'll be applying through UCAS and all the information on that process can be found here.
Universities will be asking for an A level (or an equivalent level of qualification) in biology at least, and most will want another science such as chemistry, physics, or maths. As with most sciences, you won't be expected to put together a portfolio or anything like that, but you might be asked to go to an interview - especially at top unis.
You can find an up to date list of degrees in microbiology here.
If you're not sure you want to leave behind the other parts of biology in favour of microbes just yet, you can also expect a lot of broader degrees to have microbiology modules - keep an eye out for microbiology as a module choice in biology, medicine, medical science, biochemistry, genetics, and biotechnology degree courses.