i'm new to sharepoint, so don't judje me strictly. I have a site where i need to set some permissions, but the issue is that for some libraries and lists I need to set some "access denied" permision or at least disable ability to download or open documents in library for some group, and I don't know how to do it. I looked at limited access, but it still alows to open documents in library ans i'm stuck. Any ideas how to solve this?
You need to Break permission inheritance on a list or library and than assign unique permissions only to users/groups that will have to read/edit documents in these libraries. Check this article for more details about adding permissions.
Once permissions are revoked these users will not see these libraries and documents stored there.