How to capture portion of screen on mac.
Press Command + Shift + 4  and relase the keys.
Drag the mouse to capture the screen. Png file will be saved on the desktop.

Macbook has good power backup. Upto 5 hrs. Configuring Hot Corners might help you save even more power on mac.
1. GO to System Perferences.
2. Click on Desktop and ScreenSaver option.
3. Move to Screen sever tab.
4. On the bottom you can see Hot Corners button.
5. You can configure four different options for each corner.

6. Now you [...]

Here is the way to increase system font-size in mac.
1. Right click on the desktop.
2. Click “Show View Options”.
3. Now you can see the box to change the system font-size, size of the icons etc.