Cisco Firewall

I am entirely confused, and online documentation that I found does not really addresses my question.

I have 3 PC on the inside 10.0.0.0/24 I have 1 server on the outside 205.0.0.1/24

How do I build the access-group if I want the inside to be allowed to reach the outside, vice-versa? In what direction and interface do I build the access-group? What’s the logic behind this?

Do I place it on the inside or outside interface And which direction do I sit this on?

access-group INSIDE in interface INSIDE

access-group OUTSIDE out interface OUTSIDE

Each interface has (2) options. Either in or out. How do I know which to select, what logic do you use to help you simplify this logic?