Simply put, Illustrator deals with vector graphics which can be scaled to enormous sizes and look nice, while Photoshop deals with raster / pixel graphics.
(If you are not familiar with those two, I can explain further.)
If you ever used the pen tool in Photoshop, making points and curves, that's Illustrator's 'main' tool.
I started Illustrator a few months ago and didn't find it too difficult to get into it (even tho I'm still not a master ) I personally like Photoshop much much more, it's intuitive and straightforward, while Illustrator feels more like work, but that's just my personal experience.
There are many tutorials online, I found this free course very helpful as it covers all the basics very well.
Hope this helped, feel free to ask anything more if you want!