Breeding bettas takes a lot work, money and dedication.
You need to have the right setup, tools, FOOD, and the willingness to dedicate a lot of time to these fish for the next few months.
The best way to start... read, read, read.
There's a lot of goof information out there on how to breed bettas but it's not something to be taken lightly. As you found out, bettas can really hurt eachother if the proper conditions are not set before attempting breeding.
These are good sources of information regarding betta breeding:
(very good for beginners)