You can start and use GameMaker without making an account. You will be asked to create an account when you create an executable.
Use the Version & Account Details menu to sign in before creating executables. You can use an Opera account to sign in, or use a Legacy YoYo Account.
You can read the following page for information on how to obtain licences for GameMaker:
IMPORTANT After purchasing any new licence for GameMaker, use the Update License option in the Version & Account Details menu so your new licence details are loaded.
You can use a Legacy YoYo Account to sign into GameMaker. This will open the following window:
If you require proxy support for your installation of GameMaker, this can be added simply by clicking Proxy settings. This will bring up the following window:
You can now add in your proxy details. Some of the fields shown above are optional and if there is one you don't require then simply leave the field blank. Before continuing however it is worth noting that if you have set a proxy in your Windows Internet Options, and it doesn't require a username/password, then it should just "as is" and you probably will not be required to set up the proxy in GameMaker.
If your proxy does require a username and/or password, then you'll need to add them in to the fields shown in the window above. Note that in these cases the username/password/proxy details will always be required, and that the proxy IP should also have the port added, ie: xx.xx.xx.xx:port.
Once you have added the relevant information, click on OK and log in to GameMaker.