It's simple, first check the exchange at coinmarketcap. and I choose MEXC a few days ago to bought it. Make sure withdrawal menu is not locked. You can check it at CMC with red cross symbol. Lastly, make sure of the TON coin network because it has the Eth, BSc/bep20 and TON networks. Just adjust it to the wallet you use, for example if you use tonkeeper you use the TON network.