So if i bump the first tx, the second one is just cancelled and my coins will be back
Yes, it would be like that the second transaction has not been made at all.
If my second tx is confirmed, the first one will be confirmed, so i can only bump the second one ?
Again right.
Your second transactions is spending the fund received in the first transaction and that can be confirmed only if the first one is confirmed too.
If the fee paid for the second transaction is high enough, miners will include both transactions in the same block.