Besides VS Beside

It is quite important not to confuse them, for they are different in meaning and usage. 

beside 

Beside is a preposition, similar in meaning to 'next to', 'at the side of' or 'by':            

• 'Where is the apple orchard?' 'It’s right beside the main road. You can’t miss it!'
• 'We were lying beside the pool when the phone rang. It was his boss wanting to know why he wasn’t at work.'

It is often used with verbs such as 'standing', 'sitting', 'lying'. It is also used in the expression beside the point when referring to something that is not relevant to the subject under discussion:

• 'Modern art isn’t really art at all!' 'That’s beside the point when so many young people respond to it with such interest. They regard it as art.' 

besides

Besides is a preposition, meaning 'in addition to', 'as well as' or 'apart from':

• 'What exam subjects are you taking besides English and maths?'
• 'Were there any boys at the party besides Matt and Dillon?'

It can also introduce a participial phrase:

• 'Besides bruising his face, he cut his lip and bloodied his nose.'

Besides also functions as an adverb, meaning 'as well', 'furthermore' or 'anyway'. It is often used to introduce an afterthought. Consider these examples:

• 'It’s too late to start a round of golf now. We shall never finish before dark. Besides, it’s starting to rain.'
• 'He doesn’t have very much money and he doesn’t have very many prospects. Besides, he’s far too young to think of getting married.'