What exactly are you trying to do?
Note that in "Airplane Mode" all the radios are turned off. This includes the cellular radio, GPS, Bluetooth and WiFi (which includes WiFi Hotspot).
However, you can turn the cellular radio off and keep the WiFi turned on and use that if that's what you are trying to do (if you are connected to an external WiFi source) although you really don't need to. If you are connected to a WiFi source, the device will use that by default. Note also that you can use the device Settings to prevent applications from using Cellular Data so that they will only use WiFi data.
Note that tethering is not free but might be included in your plan depending upon the plan you have. Note, however, that data used while tethering will count toward your data limit.
You mention "the hotspot option". Can you elaborate as to what you mean by that because typically that involves using the device (your phone) as a WiFi Hotspot for a second device? But that doesn't seem to be what you are talking about trying to do.