Assigning Applications to Specific Spaces
By default, when you launch an application, it will launch in the space that you're working in at the time. In many cases, you may want applications to launch in specific spaces rather than in the current one—either to keep the current one uncluttered or to keep similar applications grouped together. Fortunately, you can assign applications to specific spaces so that whenever you launch them, they launch in the appropriate spaces automatically. This is especially helpful if one application launches another (such as Mail launching Safari when you click on a link in email).
To assign an application to a space, click the Add (plus sign) button beneath the Application Assignments listbox and use File > Open to select the application. Then, from the pop-up menu next to the application's name in the listbox, select which space you want it to use (the space will be highlighted in the preview).
If you later decide to reduce your spaces in a way that removes a space that has applications assigned to it, your Mac will alert you and offer the option to either cancel the reduction in spaces or to continue. If you continue, the applications will be assigned to the nearest adjacent space.
You can also assign applications to every space. This means that no matter what space you're working in, you'll see that application's windows (much like you see the Dock and desktop items in every space). This is a great option if you always want to have an application visible while it's running.