Building dirt jumps requires a lot of time and your own land you can build on. If your building on someone else's land make sure you have there full permission first.

Building dirt jumps takes a long time to master and as your jumping skills improve so will your building skills.

First you want to find somewhere to build, where you can take shovels every time you go or leave them there.

Once you have a place to build and path cleared out then you can begin building. 

Then start digging and make 2 mounds of dirt one will be the landing and the other will be the launch or lip.

The landing can have logs since you won't be carving from it or molding its shape

 much.

Land

Shovels

Time

Make the 2 mounds about a foot bigger then you want the jumps to be, because you will pack them down do they don't fall apart. If the jump is 3 ft tall you want about a 6 ft gap. You can make it bigger or smaller depending on how far you go when you go off and how you carve the lip. After you finish one jump and get good at jumping it you can add a second behind it about 12 footsteps from the end of the first jumps landing make the 2 mounds again for you second jump. When you finish building it, start digging between the two jumps so you can pump between them. It allows you to maintain speed.

 You'll want to make the 2nd jump a little bigger then the first. Once you master jumping both of them make a 3rd and you will have a six pack. Then you can make them bigger or add more jumps on the end. Making them bigger will allow you to get better at handling air and rhythm. Making more jumps will make you a better rhythm jumper but you won't get the experience of bigger air. You could build a lot of bigger scale jumps and you could learn to handle more air and rhythms better.