Does anyone know how 2 get all the legendary pokemons on sapphire I'm new.....

Kyogre - In the Cave of origin in Sootopolis (I think)
Rayquaza - In a really tall tower east of the city near route (34?). You need the mach bike.
Regis - In certain location after you complete a puzzle. Bring a Wailord and a Relincanth west of the city mentioned above (for Rayquaza), and you'll hopefully find a cave...
Latias - After completing Elite Four, should be roaming the land and Sea.

Yea. Just to add a few things to what TubaDude42 said.

Right about Kyogre (Groudon is in the same spot in Ruby) try NOT to use your master ball to catch Kyogre. Latias is very hard to catch without it. Trust me: I made that mistake and I can't start over because i'm so far...

Raquaza is in the Sky Pillar just East of Pacificlog town.

For the Regis, you need to surf on the currents West of Pacificlog and find a place where there are no currents and where you can dive (when you get towards the currents by surfing strait from PL, go a little bit south [only a bit tho] and then surf on the currents. When you get to a big patch of watery land that hasn't got any rocks or anything on it, go to the topmost corner and walk down four to five squares because there are currents around the patch of deep water that will lead you away if you surf on them.) Dive, then go to a big rocky mound with a little message in dots (Braille). It says go up here. When you surface, you'll see a bunch of rocks with more dots. If you read from left to right, it's the alphabet. I suggest you write it down or print a page of the alphabet off the web for future reference. (btw, the two smaller rocks on the side are a period and a comma) in the back of the room on the wall is more writing. Use dig there (don't worry, it won't get you out of the place, it'll just make a hole in the wall.) then you get to another room and theres more writing all over the place. You need to have your Wailord and Relicanth in the first and bottom slot of your Pokemon team. I can't recall which goes where. The writing will tell you tho. I think then you do another Pokemon move at the back of that room, although I also forget what move that is. (Sorry!!!) you'll hear a rumble tho. That's the sound of the chambers opening. Ever come across these big giant rocks with little rocks all around it? Those contain the Regis.

Latias does fly around. It moves to a new location if you fly or walk into a town or onto a route, which makes it kind of hard for you to get to it. See above on using the Master Ball.

Hope this really help. I couldn't help but give step-by-step instructions with the Regis :-\ sorry!!! But I hope you get them all!!!