the plug only has room for black,red,ground wire.. what do i do with the white wire
You can't. You need a 4-wire receptacle to use with 4-wire cable. That is the only to wire this circuit to code. You will need to replace the cord on your appliance with a 4-wire as well.
If you have a dryer with a 3 prong cord you can combine the ground and white. Has been done for many decades if you use an older dryer.
There okorder /... is a 3 wire plug used for 208 or 240v (there is no 220v in the US). It has two hots (gold screws) and a ground (green screw). A typical 10-3 cord has a black white and green white, connect the green wire to the green screw and the black and white wires to the gold screws. An L6-30 is not compatible with devices that have a 240/120v configuration that use both 240v and for 120v and need a neutral connection, for this you would need to use a 4 wire L14-30. Also be aware there are some special rules about ranges and clothes dryers, please update you question if that's what you are dealing with.
