Depth of Market, aka the Order Book, is a window that shows how many open buy and sell orders there are at different prices for a security. Let’s say the current price is $1, the DOM will show how many orders there are at $0.90, $1.05, etc. It’s a great tool to see where the supply and demand levels are.
Main parts of a DOM window explained
Cells  for placing an order
Bid  / Ask  Volume
Profit/Loss  for all open positions. By click on it, you could change view - money/pips/%
Posizion size 
The data is streamed from the broker. The data in the DOM and the chart may be slightly different since various data sources are used.
Data is shown in a semi-static format. This means that the price rows are fixed while the price moves within the shown range. If the price moves above or below the visible range it’s recentered after 5 seconds. The 5-second timer is the middle icon, and you can recenter the current price immediately by clicking it .
To look at prices above or below the visible range – use your mouse wheel, drag a cell up and down, or use the navigation buttons under the row.
To place a market order simply click Buy Market or Sell Market. The number shows how many securities will be bought or sold, you specify that at the top of the DOM window . It also syncs with the floating trading panel.
You can place orders at a specific prices To buy – click the cell at a price you want in the left column, to sell – in the right one.
These orders will be Limit or Stop orders by default. Logically, if you want to buy below current price it will be a Limit order, and to buy above will be a Stop . For selling – above price will be a Limit , and below is a Stop. The picture below illustrates this.
If you want to place an order which is DIFFERENT from the defaults described above, hold the CTRL button on your keyboard and click the cell you want. The order type will be reversed Stop ↔ Limit.
You can use the right-click menu to place an order:
By default there’s a Confirmation dialog that pops up. If you want to turn this off, you can do so in the settings.
1. Click the label with the number next to the DOM – this is your order label. You can then change any settings that you like, and click MODIFY.
2. Click and drag the order label to another price level. The same dialog will pop open.
Active “Limit Buy” and “Limit Sell” orders are green.
Active “Stop Buy” and “Stop Sell” orders are red.
Active “StopLimit Buy” and “StopLimit Sell” orders are yellow. The limit level of such orders is duller in color, and the Stop level is more vibrant.
If you are in a position on this symbol (you either bought or sold some), your position size  will be shown as a number at the top of the DOM. If you bought (in a long position) the box will be blue, and if you sold (in a short position) it will be red.
Long position (you are hoping the price will go up!)
Short position (you are hoping the price will go down!)
To close the position or reverse it, use the Flatten  or Reverse buttons at the bottom of the DOM.