Different kinds of LTE sessions ?

[tronar]

Hi, I'm struggling to understand the different kinds of connections that a device can mantain.
I'm programming a T-SIM7000G and kind of understand that in LTE you may have more than one PDP context with different profiles.
I also understand that the modem supports high level protocol sessions that use some form of high level session object.
But I have not been able to clearly understand which is related to what:

AT+CGATT (network attachment aka registration?)
AT+CGACT (PDP session ?)
AT+CNACT
AT+SAPBR

And I'm leaving high level ones like IP/MQTT/HTTP.
Is there any document that describes these ?