Eva,
The post by Chris Smith is right on. What those minerals are worth today could be a fraction of what they will be worth six months or a year from now. I would start by reading everything under the "Mineral Help" category on this forum. Attractive offers mean nothing if the party making the offer is planning to snooker you on the lease terms or doesn't really intend to deliver the money. It happens all the time. Be careful and don't sign anything until a qualified oil and gas attorney or a professional manager (not a landman) has read the contract. Also, don't cash any unsolicited checks that come in the mail and don't tell the landmen that there is a price you might accept without them making an offer first.
Best of luck to you!