There was typically first a blockhouse, because it could be made pretty quickly. This would be essentially a log cabin, but with small ports in the walls instead of windows, and an overhanging second level with gaps in the floor that allowed the defenders to defend the door and also be able to put out any fires built against the walls. The blockhouse was also often sited on a higher elevation, to give a commanding view of the area. The US Army Education Center in Carlisle PA has a small reconstructed blockhouse and a bit on the construction here.

A blockhouse could resist a raid, and resisting raids was the most common use of a fort on the frontier. But a blockhouse was also small, and as the colonists moved west and encroached on Native Nations, if there was a raid there would be numbers of families as well as their animals "forting", or needing shelter. Blockhouses would therefore often be expanded into forts, anchoring a part of a palisade wall. During the French and Indian War, George Washington also had a series of forts constructed along the western frontier of Virginia. Built for accommodating a militia force, these were often more elaborate than a blockhouse with a simple palisade wall, having features like bastions and defensive trenches, and probably emplacements for light cannon.

I am not aware of a big book covering all frontier blockhouses and forts ( maybe someone will stop by here who knows one) but there are ongoing archaeological digs of old fort sites, and the reports are interesting reading. One of the more important forts in western Virginia was Arbuckle's, which became a staging point for the colonists' forces at the Battle of Point Pleasant. You can read the report of the dig here, and there's a website here for the Fort Edwards dig, further east on the Cacapon River. You might also be interested in the drawings Washington himself made for forts here, now in his papers at the Library of Congress.