You'll need a mercenary digi-egg and data. The type of data is based on what type of digimon are you going to hatch. Next, you'll need to successfully insert data at least 3 times to hatch it. Sometimes data insertion fails so you'd probably need to get more that the needed amount. You can insert data until level 4 or 5 but be careful not to break the egg. The higher the level, the better digimon you'll get but getting it to a higher level is going to be hard.