1. Open the Minecraft Launcher: Launch the official Minecraft Launcher. 2. Go to Installations: Click on the "Installations" tab at the top. 3. Create a New Installation: Click the "+ New Installation" button. 4. Name Your Installation: Give it a descriptive name like "Minecraft Beta 1.7.3" so you know what it is. 5. Version Selection: In the "Version" dropdown menu, scroll down until you find "1.7.3" (or the specific Beta version you want). It will be under the "Legacy" section.