Don't worry. There is a learning curve, like the first time you used a windows computer. For a few weeks you'll be trying to do things the windows way, when a faster and neater way is often available. It will happen, but eventually you'll get the hand of it all.
Firstly -- the router password. I assume you've clicked the wireless icon in the menu bar at the top, and clicked on your network's name? If so, and if you need a password, it'll ask you for it -- this is where I assume you've got it. If so, then you do need the router password. If you don't know it, you'll have to reset the router. You can turn the router upside down and find a small recessed button that you'll need a pencil or similar to press, to reset. This restores the router to factory settings, so you can enable wireless and security again, and choose a strong password which you should write down and keep somewhere safe. Then try connecting with your other computer, or your macbook.
As for the maximising thing -- it doesn't work quite the same way as windows, and this at times can be annoying, but usually it's fine. Top-left are three little 'traffic light' buttons. Red closes the window, amber will minimise it to the dock, and green maximises it. Maximise here though means 'make the window as large as you need to', and not 'use all the screen'. You can always resize with the bottom-right corner of the window.