H hot key

You need to select the part of the mesh you want to hide, the press H.
If this doesn't work, check you don't have an add-on or other software that uses the H hotkey, for example GPU software.

What do you mean by box out?Are you trying the Control + B to box hide stuffs?

In object mode with an object selected H will hide the object. In edit mode you need to have faces, edges or vertices selected then H to hide your selection.

And then there is also the one, that everybody is always forgetting, ...(drum roll)...:

ALT+B (works in Object and Edit Mode), to Box Select a part of the Mesh you not want to Hide, something like this:

It's called Clipping Region, btw.

In Sculpt Mode, there is a Box Hide, but it doesn't have a Shortcut...:

To select the edge loop that you want you have to click on the edge that points in that direction. 

If I want to select this loop that goes like this:

Then I click on an edge that points that way like this one:

If I wanted a loop that goes up:

Then I click on an edge that points in that direction:

Zoom in, and (in Wireframe Mode) be very careful where you have your Mouse Pointer, when selecting and Edge Loop with ALT+Select (LMB, or RMB, depending on your Preferences...LMB is Default).

You can also hover your Mouse Pointer over a part of the outer Mesh and press L. Then press H to Hide. That will make Selecting things on the Iris a lot easier.