The Unreal Project Browser displays when you launch Unreal Engine (UE4). It provides a starting point from which you can create projects, open your existing projects, or open sample content. To open an existing project, select the project from the Recent Projects area. If your project is not displayed under Recent Projects, click More to display all available projects.
Once you have selected the project you want to work on, click Open Project. You can also double-click the project thumbnail to open it.
If you want to bypass the Unreal Project Browser, you can click More to expand the Recent Projects area, and check the box for Always load last project on startup. The last project you worked on will now open when you launch UE4.