A proxy server is an application between you and the Internet (eg. a computer or virtual machine) that hides your IP address. By using it, you are able to mask the activity to make it appear as if it was originating from a different location.
Proxies are used to access region-locked content and to remain anonymous online, as well as for nefarious activities including fraud.
VPN stands for Virtual Private Network. This method allows you to create a secure connection to another network over the Internet using software built into your operating system or a 3rd party application / service.
VPNs are often used to access region-restricted websites, shield a person's browsing activity from prying eyes on public Wi-Fi, and more. They are also used to cover nefarious activities, such as click fraud.
What's the difference between a proxy and a VPN?
A proxy does not encrypt data, meaning it will not increase security, while a VPN does.
Tor browser is an application that comes with built in anonymization features such as VPN, encryption and blocking of tracking.
The idea behind the project is to protect the common people from tracking by various government and private enterprises. However over time it became super popular with various malicious and nefarious users. It is often used for click fraud.