I want to learn OpenWrt, I came to know that i can also install OpenWrt on PCs like HP T620, Dell Wyse 5010. I believe its a better choice as there could be lots of limitation while using some particular router.
I want to know what are the other low cost options i can use,
I will be thankful if someone also advise me resources to get start for a dummy person.
Depends on where you are, geographically.
But you should really read Tips for getting cheap used x86-based firewall with full Gbit NAT (a PC Engines APU) if you are in the US
If you are from Pakistan, you need to search local markets for the relevant cards.
Having two Ethernet ports makes running the LAN->WAN router use case much simpler. With a thin client with one port you can run "one armed" with a managed switch, or use USB-Ethernet adapters like many do with Raspberry Pi.
The T620 does look quite good on energy usage. If you already have one it could certainly be used. If you're going to buy something look for a mini PC with two or more Ethernet ports.
If you want to experiment on an existing PC, you can do this:
Even better/easier to boot it from a flash drive, it won't touch your existing storage.
how to flash the liveUSB? which live USB creator to use for creating Live OpenWrt?
Any image writer (or dd) should work, I usually use Rufus.
and download any of these images?
https://firmware-selector.openwrt.org/?version=22.03.0-rc5&target=x86%2F64&id=generic
the combined, but you need to make sure you pick efi or non-efi, matching the hw.
it is with Luci included?
In stable and RCs, it should be.