Liberty is simply the concept that all individuals have natural rights and that those rights should be respected, by other individuals as well as the government. Socialism is a system that has sparked lots of media attention, but has never actually worked. Though Bernie Sanders has used many European nations as models for "democratic socialism," many of those nations have come out saying that they aren't socialist in the least. If you want to see socialism in action, just check out Venezuela and see how they're doing.
In addition, socialism not only is incapable of functioning without negative results, it also directly violates liberty. All people, regardless of race, gender identity, religion, sexuality, etc, have a right to go out into the (preferably free) market and make as much money as they can and choose how they want to spend that money. Taking it away from you and giving it to someone else is stealing, and violates the individual's right to business, and therefore violates the concept of liberty. I am not, however, saying that we should never give to the poor; that's why we have things like charities and food drives and donations. That is voluntarily giving to the poor. Taking your money and giving it to the poor without your permission violates natural rights and is also inefficient, as proven in the previous paragraph.