Break it down into pieces. Some devices are only used as capacitors. Some are only for limiting voltages and the rest is only a very simple bias and protection voltage generation circuit. It is basically what adamantiumxx told you to analyze. You can find analysis in any CMOS circuit design book.
You might want to wait until you cover this stuff in class. Freshman year you should only see sources, controlled sources, and discrete components.
Do not remove the vdd2v5. This is likely due to a drain source voltage limitation of these .5um transistors