Lucy,
If you have roads that eventually lead to another civilization's capital, or you have a sea trade route (via harbor) to another civilization's city, you can trade with them. See the Trade Advisor (F2) to see with whom you can trade.
Next, you need things to trade: Resources or luxuries. If you have extra ones of these things (e.g. two spices attached to your trade network), you can trade them with other civs via the diplomacy screen. Note that for a resource to be 'yours,' it needs to be within your cultural boundary and connected by a road to your capital. Or you have a colony on the resource/luxury connected by road to your capital.
If you have roads that eventually lead to another civilization's capital, or you have a sea trade route (via harbor) to another civilization's city, you can trade with them. See the Trade Advisor (F2) to see with whom you can trade.
Next, you need things to trade: Resources or luxuries. If you have extra ones of these things (e.g. two spices attached to your trade network), you can trade them with other civs via the diplomacy screen. Note that for a resource to be 'yours,' it needs to be within your cultural boundary and connected by a road to your capital. Or you have a colony on the resource/luxury connected by road to your capital.