At the beginning. when nobody owned bitcoins. what was being minned? what I understood about mining a block is that,
New/pending transactions are to be verified and placed into a block solving the proof of work.
The miners are rewarded for this task.

In the very beginning.. when there were no transactions taking place.. what were they mining? what were in those blocks?
how did bitcoin circulate all over the world?
The first blocks were completely empty and didn't contain any transactions.
The first transaction was in block 170 from Satoshi to Hal Finney, as seen here.

As newly generated coins from mined blocks are only spendable after 100 blocks, the earliest possible block to spend the first coins would have been at block 101.

It is completely legit to mine empty blocks (even if there are pending unconfirmed transactions). Here is an example of an empty block on April 2017.