Thank you Josh!

I would say to use 'inside' when the alternative is 'outside'. For example: Do you want to eat inside the restaurant, or outside? Please color inside the lines (as opposed to outside the lines). 'In' is more of a simple direction. Examples: Let's go in the restaurant. Put the gift in the box. In these examples, something is already out. I'm not an English teacher; these are just my opinions! Good luck!