Socialism, social democracy, and communism all focus on a more egalitarian distribution of wealth and income. To what extent and what their approaches are, differ, though.

Social democracy proposes a classless society, usually within the premise of an 'electoral democracy', often with trade unions, collective bargaining, worker representation, and strikes as a bulwark against further deterioration into capitalism.

Socialism, if distinguished from social democracy, also wishes for a classless society, but it goes further: it wishes to advance social ownership of the economy.
Rather than just politics, the economy is also fully democratised. Instead of a CEO possibly deciding for all, it's the labourers that choose, that have a say.

Communism proposes that a just society must be not just classless, but also moneyless and stateless.
Instead of money as transferrable and susceptible to wealth accumulation, other means for exchange are used; labour vouchers, community exchange systems, and so on. Instead of a centralised, repressive state, society would be decentralised and free, living in communes; if there is a military or a police, both should stand on equal footing with the people.

Personally, I'm an anarchist communist and favour that model, though I also can see a case for market socialism or council communism, and feel sympathetic to the left wing cause in general. And that is what all of us should do: respect each other's outlooks, and strive together for the left cause. The greater the strength is there, if comrades complement one another, supporting each other under the red banner.