If you have never been on Zoom before, you will need to register with them. This is free. You are advised to do this 15 or so minutes before the meeting starts, to give you plenty of time to complete the process.
Click on the meeting link given on the Open Door page. You will be taken to a page that says:
A download should start automatically in a few seconds.
If not download here.
If you cannot download or run the application, join from your browser.
If you have problems joining the meeting, see probable solutions.
There might also be an orange panel with an arrow in it in the top right hand corner. Ignore this.
The "download" will be the Zoom app that enables you to join any Zoom meeting without giving your details each time. It is unlikely to download automatically, in which case click on "download here". This will place an installer in your downloads folder. You click on this and it will guide you through the download process.
If you do not feel confident with this, or know where your downloads folder is, instead click on "join from your browser". This takes you to another panel where you need to enter your name. Fill in the boxes, tick "I am not a robot", click on "join" and finally you will be asked to agree to Zoom's terms. Once you have agreed you will be taken to the meeting. If you are early, just wait for the meeting host to start the meeting.
Old computers may not work with Zoom, or you may have to click on "probable solutions".