when i try and copy a shape from illustrator and paste to photoshop it become all pixelated I know I might be doing something wrong but somebody help me with this situation
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Adobe Illustrator is a for Vector artwork and Photoshop is for Pixel artwork. The differences are now less obvious as they have each become much better in the other area, but there are still differences.
To give you an example, here is a 10px x 10px circle on a 20px x 20px artboard, displayed in both Vector and Pixel format.
Illustrator presents the circle as a perfect circle at any magnification, because that is how vectors work. They are made to scale infinitely.
Photoshop, on the other-hand, is designed to create art at a particular scale. So it is (correctly) showing you how the circle is represented at THAT scale. If you were to instead create a circle that is at the resolution of your screen at 100% (the examples I gave displayed at around 230px x 230px) then it would be indistinguishable from a vector at THAT size.
Like Luke said, Illustrator is vector while photoshop is raster. The best thing you can do in this situation is to paste from illustrator into photoshop as a smart object. By doing this you still retain the ability to edit the original vector.