I have my laptop with RTX 4090 graphic card. How can I mine bitcoins with this card?
You need ASICs to mine a decent fraction of bitcoin. Not just one but multiple running with good ventilation, cooling and power supply. Forget about GPU, those days are long long gone. Rather use that device for playing games.
How long can I mine one bitcoin?
It is better you buy bitcoin directly and hold it to sell at higher prices.
Please help me or send me some.
Let me take the moment to remind you of the rule that begging in any form is not allowed. If you want advice, then buy bitcoin at the low price once you have a stable income.
I'm a newbie in crypto.
You will learn eventually. Mining is not a get-rich-quick scheme. Anything that advertises itself in that manner is a scam.