After some of the introductory scenes, you’ll gain control of the main character. Speak to the two ladies on the right for a quick scene, which will prompt you to name the protagonist (default name is Tidus. Afterwards, you’ll end up on a highway overpass. Run along it for a while; as you go along, speak with everyone on the way - one (a girl in a pink shirt) should yield you two Potions , so long as you tell her you have some spare tickets. Eventually, you’ll be allowed to proceed into the blitzball stadium at the end, although you will have to push your way through the crowd.
When you return to controlling Tidus, you’ll have a pretty clear path to go along for a while. On the way, you’ll meet up with Auron - he will ally you for a while, and he can be quite the physical powerhouse. In any case, continue along the path outside of the stadium. After a strange scene with the hooded child, continue along the path to Auron again. This scene will culminate in a battle with Sinscales, which are pretty weak but this will be your first battle in the game. You’ll also get the Longsword weapon from Auron during that fight, which teaches you the basics of FFX battle.
Battles in FFX are turn-based and the turn order will be in the upper right corner of the screen. There’s really not any special attacks you can do at this moment, but skills and magic will typically cause your next turn to be delayed or quicker, depending on the action and strength of them. With this in mind, there will be some strategy involved in battles as you progress through the game. Since you can’t do much right now, just select the Attack command, which should be enough to deal a killing blow in one hit to a Sinscale.
Continue along through the groups of Sinscales. The second big group of Sinscales will be both in front of you and behind. Heed Auron’s warning here and worry about the ones in front of you, as the ones behind will continually respawn. While you might think this is a good grinding spot in the beginning of the game, the Sinscales will award you with nothing, so it’s best to cut down the ones in front and move on. You should be more than fine in not having to use a Potion, as their attacks are weak enough and they should hopefully only get one or two attacks off on you. Eventually, you’ll encounter something a bit…bigger.
BOSS - Sinspawn Ammes
You’ve already dealt with the Sinscales thus far in the main game, so you should be familiar with their simplistic offense. Sinspawn Ammes is different: it relies entirely on Demi. Thankfully, Demi will not KO you, as it will only take away 25% of your current HP value. This battle opens up with Auron having his Overdrive, which are like the Limit Breaks of this game (for those that have played previous FF games). These attacks typically deal higher damage than normal, sometimes deal additional effects, and often can also hit multiple times. The Overdrive meter is below your HP and MP, and once it’s fully, press left on the command menu to access the Overdrive menu. Auron’s Dragon Fang requires you to press a simple sequence of buttons to induce an attack on all enemies, but you have a time limit.
Dragon Fang should be more than enough to take out all of the Sinscales, leaving only Sinspawn Ammes left. Since it will only use Demi and that spell cannot KO you, there isn’t much worry here and it’s best to avoid using Potions for the time being. Despite that, you will have at least another battle after this “boss” fight, so it might be a good idea to avoid having super low HP. During the battle with Sinspawn Ammes, you might get Tidus’ Overdrive full. His Overdrive, Swordplay, will basically show a gauge on your screen, with a cursor that moves back and forth on that gauge. You will need to stop the cursor in the golden part of the gauge, in the middle, within the time limit.
After the fight, continue along the highway overpass to the Save Sphere. Examining one fully heals your party’s HP/MP/status, as well as letting you save the game. Continue along again to a battle with some Sinscales and as you’re fighting them off, you’ll notice they will keep spawning. Eventually, Auron will suggest to attack the tanker on the right side of the screen. Strike it a few times to initiate a series of scenes. Eventually, you will regain control of Tidus, who will be floating in the air. Hold down the button shown on screen and head for the center part of the area for more scenes, bringing you to the next area.