I was in your shoes four years ago. The state put out a call to recruit lacrosse officials because lacrosse was growing at the high school club level so fast, they expected to see it become a sanctioned sport at the state level. I have been officiating high school basketball for 40-years and high school football for 10-years. If you do other sports, then you understand off-ball, officiating your primary, etc. If you understand hockey rules, there are many similarities. I didn't/don't follow hockey so some of the lacrosse penalty enforcements were a little foreign to me.
For me training was available through a local officials association. I participated in the training, have done a lot of reading, picked up the lacrosse rules app for my iPhone/iPad.
Additionally, US Lacrosse has a great website
US Lacrosse | National Men?s, Women?s and Youth Lacrosse with training videos available. There is also a fair amount of college and pro lacrosse on TV. Those games are a little different, but it never hurts to watch the game, movements of offense and defense, etc.
I did 3-high school varsity contests yesterday, 33-degrees, snow, sleet, rain, with no sunshine. Still had fun and enjoyed it. Last game went OT and was won in sudden-victory about 2-min into OT.
Good luck.