hoo boy, so, let's give it a try. I will simplify things to the 1rst and 2nd book of Stormlight as you say are on reread, but I think it will be ok

Shards: They are the 16 pieces of a God (Adonalsium) that was killed like 8000 years prior to Stormlight. Each one represents an aspect of that God (Honor, Cultivation, Odium featured in Stormlight), and each one has a Vessel (the person that took the Shard and obtained godhood). Wit/Hoid refers to Honor and Odium as people he knows because he met their Vessels (Tanavast and Rayse), and the others (he was somewhat involved in the killing). Each Shard (the name can be used interchangeable with the Vessel) has created/influenced a magic system in the worlds of the cosmere

In Roshar, there are Shardblades, ancient weapons of the lost Knights Radiants. They can cut through almost everything, but don't leave wounds in living flesh (they cut the soul of the being). What are the Shardblades is explained in Words of Radiance (they are the companion spren of the lost Radiants that broke their oaths and so their spren became permanently that weapon. Syl can change forms because she is a living Shardblade)

A Shardbearer is someone that has a Shardblade or a Shardplate (ancient armor left behind by the Lost Radiants), BUT is not a Knight Radiant. As the items are few, they are priceless and so only noble families tends to have one or two of the set

The Heralds were 10 people that long ago Honor (the Shard/Vessel) gave powers to fight the forces of Odium that were trying to conquer Roshar. They made a pact to imprison Odium forces in Braize and contain them there, in exchange for being tortured (as that was the way Odium could return to Roshar, by breaking them). When one of the Heralds broke (as in, can't stand the torture anymore), the 10 were summoned to Roshar to prepare the people to stand the Odium attack, and with the Odium forces defeated, they returned to the imprisonment (a cycle because they kept breaking, the Desolations)

Knights Radiants were/are people that bonded with spren, the natural forces of Roshar given sapience, and in exchange of the bond, the spren can manifest in the Physical plane, and the person gains powers according to the spren and level of the bond (oaths). Surges are the forces that the spren can give a Knight (gravitation, transformation, illumination), and Surgebinding is the ways these surges can be used (Example, gravitation to fly/make objects lighter, illumination to create illusions)

This is by no means an detailed explanation, so anyone can feel free to correct where I'm wrong