When you start PellesC - that is the IDE. However, I expect you mean a visual way to create GUI's. PellesC supplies Wizards that will help some. For example you could choose to create a Dialog based app using a Wizard, this will allow you to place various controls onto the dialog visually - the Wizard will then create a skeleton app for you.
You can find the Wizards by selecting 'New/Project' from the main menu.
I will stress though that to become proficient in programming Windows GUI apps, one needs to get to grips with the Windows code.
Once the app has been created double click on the RC listed below the project listing. Now you can add controls etc. to the dialog. You will need to find your way around, this comes with practice.
John