If you're new to civ, you shouldn't start by playing a scenario.
Those are :
-
not showing the full game, the american one having almost no diplomatic options nor teching
- a lot more difficult than the regular game
- really different from the regular game, meaning that after you find a way to beat the scenario, you still won't be able to beat the full game.
I suggest
- reading the manual!
- playing the tutorial. He's not very good, but at least it exists.
- play the beginning of a few games at any level to get a feeling of the game
- start a game when you feel you understand what it's about, play it out. don't spend too much time on settler level, it's not going to help you a lot.
Anytime you feel lost, read the forum

.