Open the coin page and use the Buy/Sell panel. The panel is the same for coins launched on MemeWarzone and for imported coins. A coin on its bonding curve trades on MemeWarzone itself. A graduated or imported coin trades in a DEX pool, still from the same page.
You need a connected wallet on the coin's chain. On a phone, Buy and Sell sit at the bottom of the coin page and open the panel as a sheet.