Beside - A preposition indicating the location of something. Beside means, ‘next to’ or at the side of or close to something. Beside Examples:
1. shoes are beside the closet
2. I feel lonely, please come and sit beside me.
3. I wish to sit beside Anjelina Jolie and take a picture with her.

Besides - can be both preposition and adverb depending on the context used. Besides as preposition means, ‘in addition to’ or ‘apart from’. When used as an adverb, it means, ‘moreover’, ‘furthermore’, ‘another thing’, ‘as well’. Besides Examples:
1. Besides Tom, who else has not completed their project?
2. Besides, there is more to what our eyes see.
3. No one besides a good leader can take such a call for citizens welfare.