What are the steps i need to make in order to connect my MacBook (running Yosemite) to an external screen so I can work from? I have a usb-c to hdmi dongle I can use but other than that what do I do?
Your MacBook will automatically identify the make & model of your monitor.
You don't need to do anything.
If you are only using the external monitor, select "mirror displays" in SystemPrefs/Displays & close your laptop.
If you are going to use both displays, choose the position of each display in SystemPrefs/Displays.
I recommend you buy a bluetooth speaker to put below your monitor. You get much better sound.
Make sure the speaker has a headphone jack, so you can plug into the headphone jack of your MacBook.
Why?, If you use bluetooth, you get a 1/2 second delay. Watching videos will drive you crazy.
You will need to buy short a male/male headphone cable.
Why get a Bluetooth speaker if I'm gonna get delay and not gonna use the headphone jack in the first place?
And something else, I don't think that my MacBook has a headphone jack!
What year is your MacBook? Mine is a 2017. It has a headphone jack.
You could also plug into the sound output jack of the monitor (if it has one). HDMI carries sound to it.
I couldn't get it to work though...
(I recommended a bluetooth speaker because it can run on battery power if needed)