Survival Mode is very different from Creative Mode! In Survival Mode, you have a hunger bar, health, and you can drown by staying underwater for a period of time. The hunger bar looks like drumsticks and will each drumstick will disappear in a period of time, for example: it will disappear faster if you are running around, fighting, etc. The health bar shows how much health you have left. If you jump off a high platform, you will lose a few health points. Getting hit by a sword will also lose some health(especially a diamond sword). Dangerous mobs(click mobs on top) will try to hurt you too. Also, and experience bar will show you how much experience orbs you've earned. You can earn them by killing mobs.