I had huge trouble casting that spell too, you have to be close to the city, cast the spell and the cursor will highlight the cell you're currently hovering over.  Red would be an ineligible cell, it will turn green when you hover it over a city.

Remember you have to be pretty close I don't know the exact distance

Really?  Because I tried casting it even from within the city, and the spell does not show up for me -- most strategic spells don't show up for me at all (only a small subgroup of spells I know show up, plus raise land, and teleport).

It is frustrating to feel that it takes several tries before you even know how to play the game reasonably or somewhat correctly. I don't expect to be an expert player the first time, but there is a minimum threshold for something to be fun. You should be able to a) tell what is powerful and weak, figure out how to do basic things like cast spells, and c) have a little sense for the overall strategic situation to make some interesting decisions. Feeling your way through 4-5 games before you feel like you can really start playing the game is ... ugh. This is especially true when the game takes many hours to play even once.