Beside can be used as a preposition to indicate the location of something with respect to something else. It usually indicates physical proximity or nearness.
'The dog sat beside the fire.'
'He stood beside his friend.'
It is important to note that when using 'beside' as a preposition, it is not necessary to include a noun following it. For example, 'He stood beside' is correct and useable as a complete sentence. Common mistakes in using 'beside' as a preposition include forgetting that it requires an object to follow it, and confusing it with ' besides' which has a different meaning. For example, 'He stood besides' is incorrect; it should be 'He stood beside.'
Beside can also be used as an adverb to indicate how a certain action was performed. It is usually used to indicate that the action was carried out in an incidental or random manner.
'He threw the ball beside her.'
'They walked beside each other.'