Hello @rashed0043
You should firstly read the description made by buyer, see if it matches your work line , the timeline, the budget and then after send the buyer request stating a message where you tell them about your gig and why you are the best among all other seller.
But firstly, do read the the link shared in the post mentioned above by @lloydsolutions , as it will help you get a clear overview of things.
Hope you find your answer!!