To clear an area grab wooden axe. 

right click one corner

left click other corner

//set [block type]   zero for clear or block type to set it to that block.

To make elevator  

create a shaft with some kind of block, anything but iron blocks

make lowest elevation solid iron blocks for floor

at each floor level 3 blocks up put a sign on wall opposite of door that is blank

put a button just below sign at 2 blocks above floor level.

To make portal.

create portal locations with /wpdc portal_name

make portal frame from anything and put gold blocks inside

at first portal location in front of port issue command to turn gold blocks into water portal

/wppc first_portal_name  second_portal_name water and click gold block with fishing pole

Then go through portal to 2nd portal location and turn and issue command again to go back to first

/wppc second_portal_name first_portal_name water and click gold again.

To make a buy sign

in sign test use

[Buy] for buy and [Sell] for sell

1

Item_Name i.e. Bread

$10  dollar amount