I am from India and want to use Lora but before that, I want to know a few things about bandwidth, tx power.
I am using region IN865.
I can use from any of these bands 125kHz, 250kHz, 500kHz, right?
Is there any imitation on Tx Power or I can use full power like 20dB.
No, you can use the combination of frequencies and bandwidths listed in the regional parameters of the LoRaWAN specification if you want to use LoRaWAN. If you want to use plain Lora you need to find another forum to ask questions and get answers because this forum is dedicated to TheThingsNetwork which is a LoRaWAN network.