Epoxy glues are supplied as a two pack which include a resin and hardener and are also more difficult to apply than most adhesives. They take a while to prepare and dry so they are not the easiest adhesive to use and they are fairly expensive compared to PVA glue.
When the resin and hardener are mixed they make a sort of white paste that is strong and bonds to many materials.
They are water proof and their fumes are usually toxic so safety glasses and masks must be worn. This adhesive is very common for fixing boats so it is not really seen much in furniture or cabinet making.
This adhesive is a good gap filler and is also good at bonding end grain but when dry it is very difficult to clean off wood so it must be done while still wet.
This type of adhesive has very good strength but because of its difficulty to prepare, long drying times and bad fumes it is not suitable for people that aren't experienced with using it.
It is also not a great adhesive for woodwork joints compared to simple PVA glue because of its properties mentioned above such as its price and preparation.