Well, it's a bit different in illustrator, but basically, there are two ways:
Way one:
Go to illustrator, make sure that the object you want inside is at front:
![[Image: 7b85d53f628e86ecd2782a0cca87e510.png]](https://i.gyazo.com/7b85d53f628e86ecd2782a0cca87e510.png)
I want the blue one inside of the red one.
Now then, go to your pathfinder, it can be found under window -> pathfinder
Select both objects (shift + click) -> divide (in pathfinder)
Use the direct select tool, press the outside that you don't want, and delete
Bam, it's done, this will not work like photoshop though, it will just create a shape that is exactly the same as the overlap
2nd method, the one I use:
ctrl + C on the object you want inside (blue box)
Press the red box
Press draw inside
![[Image: ca3108e1e45c81811114c9879dbf4c50.png]](https://i.gyazo.com/ca3108e1e45c81811114c9879dbf4c50.png)
ctrl + shift + v to copy in place
Press out of the draw inside again
Done
The second method, is actually placing the whole object inside, and if you expand your layer, you can change the object, so that's pretty much a mask like in photoshop