"A Spanish Conquistador, he led the first European expedition into the American southwest. He was the first 'white man' to observe the Grand canyon, and the Pueblos of New Mexico, Coronado was a great and careful organiser and scout so when he joins your Congress, all colonies currently on the map and exposed, including the area immediately surrounding them."
Coronado makes all colonies on the map visible and the area immediately surrounding them. This is a very useful ability but best left towards the end of the game when most of the major colonies have been founded and you have a strong enough military to take at least the weaker ones. It should be noted that the colonies true population will not be shown or its level of fortification. You'll have to go and investigate.
Henry Hudson (????-1611)
"An English explorer in service of the Dutch, he explored the Chesapeake and Delaware bays and the Hudson River as far north as Albany. Hudson later discovered Hudson bay and was finally killed by mutineers. Hudson bay became a primary fur trapping
preserve, and the Hudson Bay Company operated extensive trapping and processing facilities for many years. When Hudson joins your Continental Congress, the output of all fur trappers increases by 100%."
Hudson increases the output of Fur Trappers by 100%. This means more money but requires more warehouses and merchant ships. If the Furs are being shipped by wagon train you must have a road to deal with the quantity. Fur prices will plummet so it is a good idea to turn some of them into coats using the Fur Trader, these sell for a lot more.
Sieur de La Salle (1643-1687)
"A French explorer, he sailed down the Mississippi River into the Gulf of Mexico, claiming all land drained by the mighty river for the French Crown. He was instrumental in establishing French dominance of the Canadian fur trade. When La Salle is in your Congress, all new colonies automatically get a stockade."
La Salle gives all new colonies a stockade. This will increase defence by 50% but it should be noted colonies with stockades can't be dismantled. This is fine for colonies you found, but any you capture from the computer are likely to be in very poor locations. They will most likely not have any or enough forest for lumber, neighbouring Indian Villages and an overlapping radius with other colonies, thus reducing potential size. Also they may be a long way from your core colonies. So, I never use La Salle.
Ferdinand Magellan (1480-1521)
"A Portuguese explorer, he was the first European to lead an expedition that successfully circumnavigated the globe. Although Magellan himself did not complete the voyage, his leadership and daring made it possible. With Magellan in the Congress, the movement allowance of all naval vessels in increased by one, and the time it takes to sail from the west map edge to Europe is shortened considerably."
Magellan increases the movement allowance of all naval vessels by one, and shortens the time it takes to sail from the western edge of the map. He is handy but there are other more useful members to choose first. The increase means you can out run warships chasing you and move things between colonies quicker, particularly useful when you stop just one square short of the high seas normally.
Hernando de Soto (1500-1542)
"Ruthless Spanish Conquistador who led the first European expedition into the Southeastern areas of North America. He landed in Florida and explored much of Georgia, Tennessee, Alabama, Mississippi, Louisiana, and Arkansas. In search of gold, he is credited with the slaughter of thousands of Native Americans. With De Soto in your Congress, the line of sight of all units increases two squares making all units able to see as well as scouts."
Hernando increases the line of sight for all units to two squares and makes all lost city rumours true. This means soldiers and colonists are less likely to get ambushed. He is useful, but not very.