How Do I start Roblox Studio?
From Legacy Roblox Wiki
There are two ways to enter the Roblox Studio, you can either go to
Start > All Programs > Roblox
And click on Roblox Studio.
Alternatively, you can go directly there off the website. Just click on "Solo player" on a someone's Place. When the game loads, click on the little tab in the top left screen that says "Edit Mode."