Adobe Premiere Pro is a video editing program. Its key functionality is to edit video clips together. It has lots of other functionalities like adding text and transitions, editing audio and adding effects. Trimming clips and moving them around your timeline is a lot easier to use than After Effects timeline (for video editing purposes).
After Effects is a digital motion graphics, visual effects, and compositing software. For titles, shapes, 2D animations, adding special effects, After Effects is your tool. While you can create motion in the text, images, and any other layer in Adobe Premiere Pro – it is a lot easier to do in After Effects.