First add your background colour, I started off with black and then remembered it was too dark so anything other than black. Resize one of the brushes by holding S and dragging right to increase the size, then fill the background.

Add a new layer, press L for layers and go to the + button. I recommend adding a new layer for most things so if you make a mistake just delete the layer.

Create the horizon, pick a normal brush and hold shift and draw from left to right. The shift button came in handy for this picture.

Ok select the simple flat pen which is one of the default brushes. Select a grey colour and from the horizon line hold shift and draw up. Make sure you vary your pressure so you get a very random effect, you can also change the size of the pen (use S) for different size buildings, just experiment. Before the next step create another new layer for your background buildings and click and drag it in between the background layer and the grey building layer. Once you have done that just go ahead and choose a darker colour than your foreground buildings and repeat the process.

So im going to talk you through how to make the window brush. First select the simple round pen, and you will be able to see on the right panel it says "shape type" click on that and select the solid square block.

Next on the same panel click "flow" and under that tab you will see a percentage. Click the percentage and move it to about 230-250 %. You can drag it or just click and type in the number.

We now have to make the opacity random, I just find it makes it look a bit more interesting. Press C to open the controller editor. down the right hand side of the controller editor click "opacity". On the left click the drop down menu "signals". Hold and drag "random" and make sure the arrow on the random signal box connects to the opacity brush parameter.

Ok you now have your brush, select any colour you would like and on the right hand side panel next to "blending" there is a section that says "normal", click that and then select additive. This gives it a luminous look. Make sure you select the grey building layer and go onto the next step.

Hold shift again and draw up and down on the buildings, try not to put too much pressure on the pen. I think it works better if you are zoomed out more (hold Q and drag left or right) and use a smaller brush (use S)

Ok so now lets move onto the reflection side of the drawing. Select the default simple round pen, press C for controller editor and on the right hand side of this panel click "opacity". This time on the left we want to press "stroke parameters" and thn select "pressure" and drag it across exactly the same way as before. Note that if you have already made a change to one of the brushes hover over it and you can reset it to the original, you can also save new brushes in the same way.

Now that you have the new brush, you will want to replicate the colour of the buildings from the horizon down. Hold Alt to do this, and click on one of the windows. Make sure the brush isn't full opacity (change opacity of the brush by holding D and drag left or right)

You will want to hold Shift again to get the straight lines. Try and reflect the size and shape of the buildings as best you can, but it's going to be slightly random anyway as it is in water. So hold shift, start at horizon and work down, move slightly and repeat. All the time you will want to be pressing alt either on different windows or on the reflection itself. You can also neaten up the horizon a bit.

Create a new layer and make sure it is the top layer. Grab the simple round pen and set the opacity to 20% or less (use D), choose black and hold shift, this time go from left to right over the water. When the pen strokes overlap each other, it gives the impression of water, I think. All the time vary pen pressure and pen size.

Select the background layer. Change the pen colour to white, the change the opacity to 2 or 3% (use D) and use the same technique as the water.

Finally grab the simple round pen again, set the opacity to about 50% and change the size of the pen to quite a small size. Zoom in, and hold shift again. Follow the lines of the buildings, it really doesn't have to be perfect, don't add much pressure at all to the pen.

And that is that. The background I chose doesn't look great, and this was all very rushed but I think you get the idea. This is such a great piece of software and there is so much more to it than this, but just experiment with the controller editor and have fun!