"Beside" is a preposition that means "close to" or "next to." "Besides" is also a preposition that means "in addition to" or "apart from." It's can also serve as an adverb that means "furthermore" or "another thing."
Example :
1. Beside - by the side of (की बगल में), next to (उसके बाद). Eg.
Go and sit beside Mahi.
He is standing beside the electric pole.

2. Besides - in addition(के अलावा/ के अतिरिक्त). Eg.
Besides this pen, I have three more pens.
Besides Mr. Sharma, there are five more people.