How do you catch the 3 legendary dogs in pokemon silver?

Their names are Entei and Raikou, and Suicine is caught later

There is also LatiOS in the Kanto region

You have to get them down to 1 HP (false swipe is a good TM, as it always leaves the pokemon with 1 HP )

Then throw pokeballs at it.

Ultra and Heavy work well. Dusk works at night, the Masterball will work, but there is other legendarys which are harder to get.