How do I write HTML?

Take a look at some tutorials.

I want write access to a particular file/directory

Except in the case of personal directories, where write-permission is granted by username, write-permission to other directories (those belonging to conferences, seminars, research groups, etc.) is granted by membership of particular groups, to which write-access has been conferred. It's important for other members of the group to make files group readable if more than one person is to edit them.

Essentially, you should contact support with your request.

I want a web presence on the Theory system

Personal home pages are not created unless there is a particular use case, to avoid duplication of existing services, and the administrative and security overhead that generates. However, they can be added very quickly when needed. Please contact support.

I want to host a conference/project site

We can accommodate all these kinds of requests, please contact us with details. We can generally help with simple active pages for, e.g. conference registration, but we do not have time to debug or secure more complex active pages. We will also burden you personally with the responsibility of maintaining the security of anything more complex than simple email or conference registration scripts. Please consider whether you have the time to devote to this, and speak to us before starting to develop complex active pages that you intend to host here. Sites will be shut down and removed from the web if unmaintained.

I want my own project.physics.ox.ac.uk or project.ox.ac.uk URL

Both of these are possible. We will grant a request for the former on just about anything to do with the Physics department. The authority to use the latter is granted by OU ITS, whose criterion is only slightly more onerous: your project must usually be intra-departmental in some way. Please contact us for details.

In general, it is not possible to host non-ox.ac.uk domains on the Oxford network (please see here (older version) for reasons why).

I want to password protect something or restrict access to ox.ac.uk/physics.ox.ac.uk

This is certainly possible, with varying levels of security. Please contact
support.