"Buy side" means that a firm manages money (like a hedge fund or asset manager), as opposed to "sell side" (like an investment bank), which is a firm that makes a market and provides liquidity. In an institutional context, legit prop shops like Jane Street or Timber Hill, use their own money to provide liquidity or make markets. Those prop shops will teach you a lot, but they typically seek top tier talent (programmers, quants, or traders) and don't recruit much (if at all) from the retail space.
and any edge that they have institutionally won’t be shared with anyone. You will be given signals snd look to source inventory around those signals.