This guide will explain the process of setting up the Bootstrapper in a Warframe install, which will allow you to connect to custom servers.
This guide assumes that you have a supported version of Warframe. Please see here for supported versions and download instructions.
In general, you can simply double-click Warframe.x64.exe to start the game now. However, for our first run:
Warframe.x64.exe -owfServerHost:demo.openwf.ioWhile on the login screen, you also have an opportunity to visit http://localhost:6155/, which is available while the game is running. You may not find any immediately-useful options, but it's good to keep in mind; maybe bookmark it.
The OpenWF/Client Config.json file gives you many options, such as the fallback language and graphics driver. For the language, input the 2-letter code, so en for English, zh for Chinese (Simplifed), etc.
For more information, check out the Bootstrapper's comprehensive manual, which you can find online and in the OpenWF/Reference Manual.html file.