I think it depends on the age, ethnicity, and hygienic/food background they have. My gf is a 20 y/o Chinese so she eats a lot of salty and sour stuff from her hometown. How she smells like is indeed hard to explain. I find that if you let yourself sweat, then touch your pubic hair and smell it, you may get a faint idea.
Taste wise, she is VERY salty, Especially when she starts entering orgasm and releasing her fluids.I guess that has to do with her diet. She also has a bit of a repulsive after-taste. I think that it would indeed come to the same as licking your arm pits: A taste of rotting bacteria. Nonetheless, I like giving it to her cause she loves it and it helps turn her on... Of course, we switch roles after
For eating her out... Remain focused on the clitoris. Try sucking, pushing and moving around it. Switch from delicate touches with the tip of the tongue and then licking hard upwards like an ice-cream. You can also help yourself with your hands.
If you are strong enough to support her weight, tell her to sit on you and adjust movement and pressure to what she likes. Beware though, she will loose power as she enters orgasm and may eventually put all her weight on your face. So make sure to hold her up when she lets go.