How do I equip my crossbow? There's nothing in key bindings for equipping my crossbow.

Make sure it is available - in a pocket slot in your inventory. It is selected using the TAB key wheel and used with the middle mouse button.

I did that then attacked. When I attacked after selecting xbow, I fought with my fists instead. I tried multiple times to select my xbow through the TAB wheel. I keep using my fists instead.

Selecting the crossbow only places it in the quick access item slot. You fire the crossbow with the Use Quick Access Item button. You can configure it in options (main menu). I have mine set to mouse button 5.

You may have missed the last part where I noted you "use" the xbow with the middle mouse key - or whichever you have bound to that action. Don't forget that the crossbow's real purpose is for offing drowners underwater and dropping Harpies to the ground - not for fighting on land. No matter the bolt you are using - it's pretty useless.