Against is the opposite of for. It can also mean next to in position. That's when you use it in a sentence.
The rake was leaning against the shed.
I'm against racism.
Immure is to hold someone against their will. You can use this in a sentence by saying her mother was immured into a hospital.
The black cat stood out in stark contrast against the white snow.
That was a baseless accusation that you leveled against me.
She did not wish him to be prejudiced against her.Her anger, too, was still against Stephen.
Your evil cannot prosper against me.
He fought valiantly against the criminals who attacked him.
Mary Jo transgressed against her friend by not telling the truth. The previous sentence is an example of transgress in a sentence.
He was one man fighting against an entire system.
Copyright infringement is against international law.
The Hittites went out to war against the Ammorites.
The baby bear cub nuzzled against its mother.
The SS was engaged in criminal offenses against humanity.