Now of course most people know to do //wand to get the worldedit wand (Default = Wooden Axe)
A simple mechanic built into worldedit is multiple blocks, if you put a comma ( , ) in between the blocks you can create multiple blocks in a single worldedit or you can do that later on in //replace
Now back to the wand, with this wand you can left click and right click in 2 different positions, all blacks in between this position is your selection.

The simple //set command, does what the command says, sets blocks in your selection
Select an area and //set
EX: //set dirt - Sets selection to dirt
EX 2: //set gravel,dirt:1 - Sets selection to half gravel half coarse dirt

//replace has multiple uses that I use a lot.
For example you can replace something quickly into multiple blocks or just a single block if you want to see how something looks in that specific block.
You can also replace any block in the selection other than air.
EX: //replace stone - replaces anything but air with stone
EX 2: //replace stone cobblestone - replaces any stone in the selection with cobblestone

//replacenear is again self-explanatory it replaces certain blocks in the radius with another block like //replace but in a certain radius instead of selection.
EX: //replacenear 100 leaves 0 - Sets leaves in a radius of 100 to air
EX 2: //replacenear 100 log 0 - Sets logs in a radius of 100 to air
EX 3: //replacenear 100 log,leaves sponge,dirt - Turns leaves and logs in radius of 100 to half sponge half dirt.

Like cylinder you can create giant spheres full of blocks or giant spheres that are empty.
//sphere - Creates a full sphere of blocks, can be great for terraforming with other tools in worldedit.
//hsphere - Creates an empty sphere of blocks, this can used in a great way at spawn if you delete half of the sphere and create glass dome somewhere.
EX: //sphere diamondblock 10 - Creates a diamondblock sphere with a radius of 10 (Filled)
EX 2: //hsphere stonebrick 10 - Creates an empty sphere of stonebrick in a radius of 10 (Empty)

Like a sphere you can create giant spheres of certain blocks or empty circles.
//cyl - Creates a full cylinder of blocks around you, great for spawn starts
//hcyl - Creates an empty cylinder with a 1 block border, amazing for creating towers for builds.
EX: //cyl grass 30 - Creates a giant cylinder of grass in a radius of 30
EX 2: //hcyl stonebrick 10 5 - Creates an empty cylinder of stonebrick that is 5 blocks tall.