This game isn't complicated but you're lazy or want to know more about its mechanics so here you go.
Press the middle navigation button (should be a picture of a castle) to return to the top left-most tile in your control. Use the big red arrows to move the camera view.
You can only select tiles that you own; these will have a yellow underlined number on them. The number represents the number of units on that tile (if you have at least 1 on a tile then you own that tile.
Once a tile is selected (click on the number; it's a link) you can perform a few different actions. To move units, modify the number in the numeric up/down box beneath the camera control, then use the drop down box to specify in which direction you want to move. Click "Submit" and units will move to that tile. This is also how you attack other tiles: by moving units from a tile you own onto a tile with a number in red (red numbers represent enemy tiles and the units that they have on that tile).
Alternatively, you can click "Build" to view the structures that you can create on the selected tile. Different tile types will have different buildable structures, so click around to see what different stuff you can create. Each structure serves a different purpose.
Gold is used to build things. That's it. You can obtain more gold by claiming other tiles. If you have any mines in your control then you'll gain 0.15 additional gold per hour. Killing hostile NPC's such as Skeletons and then claiming the tile that they were on will bag you a bit of extra cash, too. Other player's structures are also worth 75% of their build cost.
Wood is another resource used for building things. To obtain wood claim Forest tiles; they generate 3 wood per hour. You can build Lumberjack's on Forest tiles that you own to change this +3 to +10 per hour.
Population is the number of civilians living within your settlement/kingdom/empire/whatever. You'll need population in order to create more units; structures that create units require that many of the population to convert and won't function unless you have above this amount (so 11 for barracks, 21 for castles). You can increase your population by building Houses; these generate 10 population per/hour.
Food is necessary for the survival of your creation. Your population consumes 1*population food an hour and your population will decrease by the difference if you haven't enough of it. You can get food by building Farms (or other food creating structures that exist post-writing)