JavaCard OS

I have read the ISO/IEC 7816 and ISO/IEC 14443 specifications for some time. However, I found it's a little hard for me to understand, and sometimes I was confused by the wording. Could someone here recommend any document that is easier to understand? Much appreciated.

For beginners, the ISO specifications are indeed difficult and abstract.

You can selectively read the standard.

For example, just read the APDU(CLA, INS, P1, P2,LC, data, Le), logical channel and secure domain firstly.
Then read the corresponding part when you need.