Suprising you brother can't help you more and that he is not more knowadgable if he has a tank that is setup and working well.
Move your liver rock into your tank. Keep an eye on the water parameters. Shoot for 1.5lbs of LR
per gallon. SO around 18lbs.
I would go out and get some store purchased LR
to get your total to around that 18lb mark. I am assuming that your brother does nto have a full 18lbs to give away. If you get stuff from the store there will be die off and you will have to allow the tank to cycle after thsi rock is placed in the system. Goign to take a few weeks at a minimum. I would test yoru water parameters every few days and watch you levels to see when the cycle is over.
After that I would make sure to get a lighing scheme setup and goign if you did nto do that already. I would wait for soem algae to build up and then go out and purchase a clean up crew. Let them live in there for a while and get used to doign bi weekly partial water changes and keepign the tank maintanance up.
In reality you are lookign at around 4-6 months before yo uadd any fish or coral to the tank. After you clean up crew is in there and you are comfortable takign care of the tank and your 4-6 months is up then add a fish if you want to.
But again make sure you have al lteh proper equipment. DO you have or need a skimmer? DO you have money set asside to purchase htings liek a skimmer a RO
water purifier, salt mix, foods, ect???
Trust me in abotu 90% of the cases where people use tap water to fill theri tank they end up havign issues. YOu may be in the lucky 10% but most tap waters have high amounts of phosphate and other algae causing ingrediants. RO
purifier will be the answer if your algate gets out of control.