It is a client-server application, no different than phpMyAdmin. phpMyAdmin is just a web-based tool that is typically installed on the same MySQL server that you are administering with it. You can, however, administer remote database servers with phpMyAdmin.
MySQL Workbench is what you might call a "fat application" that installs locally with a monolithic binary that you execute, rather than a series of php files that get interpreted through a web server (ala phpMyAdmin). You can install it on the local server, however to utilize it you will need a windowing system / desktop environment (DE). You will have to determine if your server has a DE on it and if you want to install that set of applications and dependencies. That brings up an entire topic unto itself which I'll deftly walk around, except to say: please don't do that.
In most scenarios, because Workbench requires a desktop environment, you will install it on a PC that is running a general purpose OS with a full DE such as Ubuntu with Unity or Microsoft Windows, among others. You will then supply it the network address and login credentials for the database server. You can administer multiple servers from the single Workbench application.