The Last Giant is the first boss in the game located in the Forest of Fallen Giants. The video below gives you some insight in to the process of getting to him as well as the boss fight itself.
As soon as the fight starts, dash straight ahead and through his legs. Do bear in mind that it is best to, depending on your speed and class, only hit him twice. Any more than that and you run a high risk of being hit by his swipe or stomp. After hitting roughly twice, roll away from him.
DO NOT get caught by his stomps. For classes in lighter armor this is almost a 1 shot. For all others it still does heavy damage. If he goes prone, you can get a few free extra strikes in.
I hope all this has helped! As well, here is a google doc (I did not make it) that could help you keep track of things
https://docs.google.com/spreadsheets/d/1hbECOaqekNSI1LcIA0wE... If you do like it, I advise you make your own copy in case the creator ever decides to delete it.
If you have any questions or comments let me know! Good luck and enjoy.