If you want to buy something, like a stock or a contract, you can say or otherwise indicate a bid to buy. If you want to sell, it’s an offer to sell.
If you want to try to buy 10 widgets for a price of $2 each, say “I’m 2 bid for 10.”
If you want to try to sell 10 widgets for a price of $4 each, say “I have 10 at 4.”
Now, if you’re happy to do both of the above, you can say both phrases, but it’s much more common to say “I’m 2 at 4, 10 up.” Note that this requires you to be willing to buy or sell for the same quantity; if you have different quantities depending on direction, then you’ll have to say the bid and offer separately.
Saying one of the above phrases creates an order, which stays active and anyone can trade against it until it either trades or you say “I’m out.”