@SiulL168 while it is possible to create an application entirely in Dev Studio, we would not recommend it. Switching between App and Dev Studio is normal, and think of the former as a more wizard-driven experience when creating artifacts. Take a REST integration, for example. While you can create potentially dozens of rules manually in Dev Studio (Connect REST, Data Transforms, Data Types, Data Pages, et cetera), why would you if the same could be done in a few clicks in App Studio? Because of this, our missions and modules don't specifically focus on either Studio.