I created a vector graphic using the latest version of illustrator then have tried opening it in an AI format, pasting it and opening it in a PNG format and it still looks quite pixelated when zoomed in at 300% (the actual photoshop image itself is about 20in x 20in, so I thought maybe because I have made the graphic so small in this big area that it would pixelate it, but that still doesnt make sense). I thought maybe because it's so zoomed in it'll be pixelated but I wasn't sure because it's still a vector graphic. I'm tried playing with different resolutions, exporting it as different types of files and opening them in Photoshop. A few websites have said tried ticking Anti-aliasing, but mine automatically ticks anti-aliasing. I'm really confused as to why this keeps happening so if anyone can help that'd be great thanks!
OK - let's get through the requisite vector-raster discussion quickly and move on:
Vector: Lines and curves defined by specific points (anchors) and the equations connecting them. E.G.: Bezier curves whose anchors have handles sticking out which can be manipulated to alter the connection equation in a manner analagous to elastic bands.
Raster: A rectangular matrix of set size per file of (typically) square pixels, each of which has one colour, and sometimes other data such as opacity and separate alpha channel and sometimes Z-channel depth.
Illustrator: a vector-based digital art program which can also use pixel art in vector documents, and which can export out both vector and raster versions of the artwork produced. PNG is raster, for example, where SVG and EPS and PDF can be pure vector.
Photoshop: a pixel-based digital art program which can also use vector art in a limited way, and which can export out some very limited vector format versions, and a wide range of raster format versions of the artwork produced.
Photoshop can read some specific vector art formats, and internally the pen tool, workpaths, shapes tools etc are all vector based: but for them to be seen in a pixel layer, you must either fill the space created, stroke the path with a x-pixel-wide pixel art line, or use a layer effect overlay to faux fill the space... for Photoshop, vector stuff is data to be manipulated to create pixel art. A Photoshop document has a set pixel-counted size (E.G. 1024 x 768) and a resolution (target DPI or PPI - say 72 for old-school screen resolution) whereas an Illustrator file's size is typically expressed in real-world units like inches (though not always).
When you export art out of Illustrator as a PNG or other raster format, it gets rasterised - that is, it is converted and is no longer vector art. This means that if you place that exported raster file into a Photoshop document, Photoshop looks at the pixel dimensions of the file it's importing and correctly scales it to the document it's being placed into: practical upshot here is that if you export from Illustrator at a low resolution and bring it into Photoshop, it will be small, whereas if you export it with a much higher resolution, it will come in larger.
Also remember, with ALL raster art, if you zoom way in, it WILL be pixelated, as it IS formed from pixels - little squares.
That said, you CAN place an Illustrator file into a Photoshop file - it still rasterises it on the fly, but it leaves the Illustrator file linked and editable, and it will be pixel-perfect to the resolution you've set the Photoshop file to - it will still use anti-aliasing, but that's preferred if your vector art has curves or lines at other than a vertical or horizontal angle.