To stand as we all know is to be in an upright position on one’s feet. Let us check this verb out in different phrases.

stand by means to support someone
No matter what happens, I will always stand by you.

stand by also means to adhere to a promise or an agreement
He stood by his decision despite his parents’ resistance.

stand by is also used to mean to wait
Kindly stand by while I fix the wheel of our bus.

However, just be careful in using this phrase. Stand by is a phrase whereas standby, written as a single word, is used as a noun to refer to a person or a thing held ready to be used as a substitute.

stand for means to represent or symbolize
PM stands for the Prime Minister.

stand for also means to favor or recommend publicly
Mahatma Gandhi stood for justice and non-violence.

Informally, stand for is also used to mean to tolerate
The principal will not stand for this nonsense. Better change this lay out.