API examples for reading HA Temp Sensors & Control HA Nexa Light switches

Hello.
Where can i find more examples on how to use the HA API ??
I have a working HA system with a number of temp-sensors & Nexa Light switches & dimmers (the temp-sensors & Nexa components are connected via a RFX433 unit). This is working fine, so now I would like to access HA via the HA API and :

  1. Read temperatures from HA temp sensors.
  2. Send on/off/dim-level commands to my NEXA light switches via HA

I have a working Domoticz system where I can do all this via the Domoticz API.
In domoticz it is very simple i.e :

**Control Nexa switch :**
http.begin(client, "http://192.168.0.52:8080/json.htm?type=command&param=switchlight&idx=22&switchcmd=Toggle");

**Read temp sensor :**
http.begin(client, "http://192.168.0.52:8080/json.htm?type=devices&rid=12");

**Set dim level :** 
http.begin(client, "http://192.168.0.52:8080/json.htm?type=command&param=switchlight&idx=28&switchcmd=Set%20Level&level=100");

But as I am moving all this to my new HA system and would like to do the same things here, i need some guidance