Uses of "Beside"

"He sat beside her" literally puts "he" by the side of "her." "Stand beside me when we go on the ride" is a speaker placing himself next to the person he is speaking to. "Our problems seem irrelevant beside the benefits we have gained" figuratively weighs problems and benefits in comparison to one another. It places one idea next to another.

Uses of "Besides"

"Besides" can be used as an adverb meaning "moreover" or "in addition": "Besides, I promised to go" and "We had three children on the trip besides." It can also mean "otherwise" or "else": "We have nothing besides." As a preposition, it can mean "except": "There is no other winner besides John." It can also mean "in addition" if used as a preposition: "Besides the one class, I have two part-time jobs."

Extremes: "Beside Oneself"

Another usage of "beside" is in "beside oneself," meaning "in a state of extreme excitement or agitation," according to The Free Dictionary: "I was beside myself with happiness." The treatise "Feminism Beside Itself" suggests that feminists are "beside themselves" with emotion.