Your first real Dark Souls 3 fight. We're so proud of you.
Dark Souls 3: Iudex Gundyr boss
This is not a proper boss battle per se, but it's challenging enough that it'll be a stumbling block for many new players.
This is Iudex Grundyr, and souls veterans will not have much trouble with him: standard-issue big guy tactics of circling, then rolling towards and behind him as he swings, will see you through most of his attacks. You can then smack him in the back a few times before circling again.
If you have to back off to take Estus, watch out for his leaping attack; it has a long range, but luckily a very small hit area, so dodging to one side works well.
When you have him down to about one-third health, Iudex Gundyr will transform into his second form - an unpleasantly common occurrence in Dark Souls 3. If you’ve been doing decent damage so far you can easily hammer him down to zero health before he has a chance to utilise any of his new abilities, just by using the same circling tactics as he transforms. If you need more time, be very wary of his new range, and circle to the left to avoid his worst attacks. Fire and magic do extra damage in the second phase, if you have something handy.
If you struggle with this fight, remember it's designed to teach you the basics of Dark Souls combat: stamina management, blocking versus rolling, balancing aggression with temperance according to your means. If you really struggle, consider starting a new save to try another class; you may find another weapon type and armour weight suits you better at this stage. Iudex Gundyr pretty much translates to "judgment battle"; this is where you prove you can play the game.
When Iudex Gundyr dies he drops a Coiled Sword. This is not equipment, but a key item. We’ll get to that later. For now, be sure to kindle the Iudex Gundyr bonfire now located where the boss was kneeling. Remember that resting here will restore all normal enemies to the areas you’ve cleared, if you decide to backtrack.
Pat yourself on the back, and let's head on over to our next goal: Firelink Shrine.
Continue via Iudex Gundyr to Firelink Shrine.