Inside Roblox Studio, you can create new games by clicking + New tab on the left hand bar. This will bring up a series of templates for you to work from that can be sorted by theme or gameplay style.

You can’t create meshes inside Roblox Studio, but you can create them inside Blender 3D (and export them into your project). Introducing Blender 3D.

Go to the links to startgrid and plane meshes and click on the url, highlight the numbers and copy Then go back to roblox studio, click a mesh part and go down to properties and paste in the Mesh id, ...

You can’t create meshes inside Roblox Studio, but you can create them inside Blender 3D (and export them into your project). Introducing Blender 3D.