In order to buy DLT-s you need to set up an account in one of those exchanges. Agrello DLT can only be exchanged against Bitcoins. Different exchanges have different options, but usually the process involves:
Set up an account on exchange
Pass the identity verification
If exchange allows it (eg. on Binance) you need to buy Bitcoins first using fiat currency (eg. USD or EUR). Otherwise you need to buy Bitcoin from some other exchange and transfer it to the exchanges listed above.