I am building a garden with 4x4x8's and have uneven ground or grade. How do I level the grade so that my garden does not set uneven?

You will need to do a bit of digging if you want the timbers to look level. If you just want the dirt level this will be easy. Do you want the timbers level too? They are pressure treated for direct contact, right?

To lay it out start at the highest point and stake it and tie a string. Now run the string to the length you want and level the string. Measure from the string down to the ground. When it gets past the 4" mark right there is where another tie will be needed and so on. Now measure where you need to start a tie at the lowest point and make sure you use 4' increments from the string down so when you start to step the ties it will come out level.

More than likely you may need to cut a tie shorter. Simply because no need to bury the one end in the ground to keep level and the finish grade will cover the partial buried part.