I have a 120 page word document that I want to open with InDesign, how do I do that?

You cannot open a Word Doc in InDesign.

You can place it in an existing INDD document: File > Place …

Use the Place command to import Word files.

Create a new document with Primary Text Frames and (usually) Facing Pages checked in the setup menu.

Go to File | Place, and find your Word doc. Click it.

You will now have a "loaded" text cursor. Click in the text frame of the document's first page. The Word doc should load and flow to as many pages as needed. If not. Hit Ctrl-Z to start over, and now Shift-Click with the loaded cursor — that will often force the full load/page flow if there are glitches in the Word doc.

Loading a Word doc for further work in InDesign has many steps and options to make it easier to get to a starting point you want (such as enabling a filter option to set and pre-set document conditions and styles), but that's the basic method to get from A to B, or W to ID.