aside, a side

Aside or aside ( one word ) means to one side; in reserve--
He put some money aside for a rainy day.
Set that aside for later.
Put your worries aside and let's enjoy the party.
Aside also means in a direction away from a particular point--
He stepped aside to let the man in the wheelchair pass by.
He walked in the direction of the house, but turned aside at the fence.
Aside may mean away from a group of people, or out of earshot--
He drew him aside to talk about the business deal they were planning.
Aside also means words spoken to an audience as though whispered, with others onstage unable to hear them--
As the scene ends, the hero steps to the front and explains his plans in an aside.
Aside also means a digression; a departure from the main theme--
Don't print what he said as an aside; just use the main quote.

A side or a side ( two words ) means one of the surfaces of a thing--
Each soldier should take up a position on a side of the house, four soldiers in all.
A side also means one out of a set of competing groups or teams--
We can play the game with four men on a side.
He refused to choose a side, and wouldn't sign either petition.
A side may also mean, informally, a dish to accompany the main part of a meal, or a condiment--
I'd like a burger and a side of fries.
I'd like a side of guacamole with that.
A side may mean a large cut of meat--
I'm so hungry I could eat a side of beef.
A side may describe something situated to the right or left, instead of the back or front--
The skirt has a side zipper with a hook and eye at the top.
The building has a side entrance, on the left.
We can serve it as a side dish.
A side may describe something that is an addition to a primary or main thing--
He has a side job, doing freelance work at night.

Now that you know that, you can say--
"He drew the his friend aside, and they left by a side entrance."