The Lights in the Sky are Stars
To try and ensure that some characters are not restricted to, effectively, being walking band-aids, 4th edition gives all characters the ability to heal themselves to a limited extent; while classes like the cleric do have a significant role in healing a party, the group is not doomed without one.
Each character gains a number of healing surges dictated by their class, and increased by their constitution modifier. The value of a healing surge is one quarter of your max HP, rounded down. Once per encounter, you may use the second wind action to spend a healing surge, also granting you +2 to all your defenses for a turn. After you take a short rest after an encounter, you may spend as many healing surges as you like.
Almost all (there are a few exceptions, but not many) healing abilities either allow characters to spend healing surges in battle without invoking their second wind, usually granting a bonus to the amount healed as well (for instance, the Cleric’s Healing Word power, which allows the target to spend a healing surge and get several extra d6 HP back – how many d6 is dependent on the Cleric’s level), or allow you to spend healing surges for one of your allies (such as a Paladin’s Lay on Hands). The primary exceptions I know of are the Cleric’s “Cure (blank) Wounds” abilities and the Artificer’s Healing Infusion ability, which allow characters to regain HP without spending a healing surge.
Characters typically take a short rest immediately after an encounter. A short rest is about 5 minutes, and after which you may spend healing surges, and your encounter powers are refreshed. You can take as many short rests as you like per day. During a short rest you can’t engage in any strenuous activity – you can sit in place, keep watch, ride a wagon, just nothing that requires much exertion.
An extended rest requires 6 hours. After you have finished an extended rest, you can not take another for at least 12 hours. Just like with a short rest, you can only perform light activity at most during an extended rest; most characters sleep. After an extended rest, your HP is refilled, you regain your healing surges, your action points are reset to 1, and your daily and encounter powers are all refreshed.