You can right click on the enemy tile to improve/ decrease relations. You can also right click on enemy tiles next to your troops during war time to attack. You have only 3 national focus (factory, infrastructure, port,decrease or increase relations), and 3 military orders to attack or do a naval attack. Division manpower is self explanatory, and division density is how many divisions are there in each tile bordering an enemy. You may not have enough manpower to fill up all the divisions and all the tiles if they are too high. By the way, I have no idea how to play as portugal, since there is not much minor power nearby that borders it to attack, so probably need to start by attacking minor powers like morocco, denmark, greece, etc. Attacking major or secondary power like spain can only occur after 1908.