Which transactions are being submitted in the very first blocks of some digital currency? This is more like general question about digital currencies rather than about Bitcoin specifically, but it still is relevant to Bitcoin I guess (at least this SE section is more suitable for this question than Stackoverflow).

I took some time to understand how digital currencies work, and it is common for all of them that transactions are submitted in blocks that are generated by miners.

And now there are dozens of cryptocurrencies out there, and all they maintain the same mining principle. But what I can't understand is that when a new digital currency is launched there are no transactions going on since there is no one trading it, which implies that there is no mining and no new coins issued.

So my question is, how does it begin? How these digital currencies develop and expand if there are no transactions initially?

Thanks in advance!
You don't need to have transactions in order to mine. A block always contains at least one transaction, the "coinbase" transaction that says where the block reward should go, but it need not contain any others.