Unable to pump air in my bicycle tube I am a new biker. I got some tubes to replace, but I am not able to identify the valve, I try to force air with presta convertor but the moment I remove it air blows off in a second. Please help identify valve and suggest how to fill air
I think its worse than that - your valve core is not there, but the thinner thread where you connect the airhose is there.
That tells me the shaft of the valve core broke off, the acorn nut was lost, and the guts of it fell into your tube.
This is what a removable valve core looks like:

Your tube appears to be like the one on the right, with no removable core.

You have the coarser thread as an integral part of the valve stem.  Had the valve core been removed, that coarser threadded part would be gone too.

Answer Your tube is dead and need to buy another tube.
The only way to save it is if those two threadded sections can be separated by unthreading the end.  And I suspect they won't because I can't see any flats for a wrench/spanner.
Sorry for the bearer of bad news.   If you want to find some less expensive tubes, search online resellers like wiggle or chain reaction.  Their Lifeline brand tubes are about $4 eurodollarpounds.   I buy them in 5 packs and keep them in stock.