Ruins are scattered around the world map. Waiting within them are a variety of random rewards, some helpful and some near-useless.
Since the map is blacked out in turn one, you'll need to send explorers to survey the land. Your initial Warrior unit should be put to this task.
Choose routes over open terrain as much as possible to maximize the area surveyed. Don't stray too far from your Capital, as your Warrior may be called upon to defend it later against marauders. At the same time, do explore far enough away to find a good site for your second City.
Look for Ruins, identify and destroy Barbarian encampments, and try to make contact with City-States, who provide a Gold reward at your first meeting. Unless you've been lucky enough to find Advanced Weapons, don't try to tackle an enemy Capital with your single Unit.
If, however, you do manage to pick up a Spearman from a Ruin and then find an undefended Capital City in the very first few turns, it is possible to overcome its defenses. Attack the City with a Safe Attack advantage, and use XP Promotions to instantly Heal. With a little luck, you can knock out an enemy Civilization and gain a new City very early on.
You may want to make this new conquest a Puppet for a while and annex it after developing Mathematics to avoid too much Unhappiness.
Ruins may provide:
- A +1 Citizen population bonus to your Capital City
- A map of nearby geography. Pretty useless.
- A map to locations of nearby Barbarian encampments. Not all that helpful.
- Advanced weapons. VERY helpful Upgrades a Warrior to a Spearman and a Scout to an Archer.
- A large Culture bonus, typically enough for a Free Policy. A great early-game advantage.
The world of Civilization is a barbarous one. Nomadic tribes set up encampments all around the map, and appear at random every few turns. Although they rarely have the numbers to capture a City, they are a real threat to your Workers and Settlers. They will also plunder your Improvements with impunity, setting your progress back several turns.
Your early game infantry should have little difficulty dealing with Barbarians as long as you do not underestimate them. While Barbarian combat values are relatively low, their Units often appear in large numbers. Don't allow yourself to be flanked and overwhelmed. Heal after engaging Barbarians...their friends may be nearby.
Barbarian encampments spawn Barbarians until they are destroyed. When plundered, they yield rewards of Gold. Barbarians are also a decent source of early game XP for your Military Units, although they top out their contribution to Unit experience at about 30 XP.