To have a successful call with someone while using a computer, you must have:
A Mac/PC/Linux/Chromebook with camera, microphone, and speakers
An Internet connection with minimum 350 Kbps download and upload speeds, though 10-15 Mbps will provide a much better experience. Check your Internet speed here.
Google Chrome, Mozilla Firefox, Microsoft Edge or Safari 11+
The latest operating systems, such as Windows 10 or MacOS Catalina
JavaScript enabled (this is enabled by default)
TCP ports 80 and 443 open (sometimes firewalls will block these ports; if you are having trouble connecting while on a workplace network, ask your IT team to check this)