Once you have been granted access to an HPC or cloud system, you will usually need to set up an account, and then log in from your own computer. This is usually done via the command line, but in some cases can be done via a web page.
For example, to log in to a HPC, you might open your terminal, and type in:
ssh myUserName@hpcname.someplace.edu.au
You may also need to enter in a password or add in the location of a password (or ‘key’) file. Different systems will require this in particular ways, and will discuss how to do this in their own specific help documentation.