To drink "na broodershaft" with someone is to consolidate friendship with a special ceremony when two of participants at the same time drink their glasses, for example with wine, with the hands bound in elbows. Then, most often, kiss. During the process it is necessary to look each other in eyes. From this moment participants are considered as good friends and have to address to each other on "you". Ritual comes from medieval Europe when the similar ceremony served as the proof of good intentions of the audience at a table.
According to another version the tradition to drink "na broodershaft" practiced between lovers. If a drink of one of lovers was poisoned by another, with a kiss the poison was transferred back to the poisoner. Thus, the kiss served as the proof that drink of any of lovers wasn't poisoned.
On Wikipedia in russian: https://ru.wikipedia.org/wiki/%C1%F0%F3%E4%E5%F0%F8%E0%F4%F2
It doesn't matter if you're a man or a woman, straight or gay, married or single, this russian tradition is for everyone in any combination!
So if you drink "na broodershaft" with someone I strongly recommend you to buy a russian vodka at first!
Have a nice drink!