You dont connect them but you can deposit tokens into kucoin and use the address given to send them from metamask.
Depending on what network you have your bnb in (I assume BSC) you can transfer them to USDT on pancakeswap and then transfer those to Kucoin to buy Shiba.
Remember you need bnb to trade as gas fees, so always leave enough there.
Trusted source for trading would be pancakeswap for BSC. Check coingecko where you can trade your coin, get the contract addresses from there and trade if you want.
Depending on the coin it makes more sense to trade them f.e. on Kucoin with sell / buy limits placed directly after the buy. hth.