The subject of a sentence is the noun or noun phrase that performs the action within the sentence. In passive sentences, the subject is the recipient of the action.
Some researchers assert that clockless processors will
soon become cheaper, more reliable, more energy efficient and easier to design
than chips based on today's prevailing technology.
--W. Wayt, "Turning Back the Clock," Scientific American (modified)
Your verb must agree with your subject in number and person.
Every sentence must have a subject. If there is no noun subject, you must use an expletive, it or there, in the subject position.
It is possible to calculate how much matter the galaxy
must have in order to hold a star in its orbit by the force of gravity.
--"The Milky Way," Compton's Encyclopedia
Not all the galaxy's stars are confined to the galactic plane.
There are a few stars that occur far above or below the
--"Astronomy," Compton's Encyclopedia