SP500 (SP500)

[G101]

Hi guys I hope you can help me with what is quite a basic qusestion,
I am quite new to stocks and wanted to know if I buy an index fund (for example vanguards s&p 500 fund) would I actually be buying/participating or own part of the companies and assets themselves directly (within the s&p 500)?
Like would I be giving money to the actual companies and taking part in their profits and affecting their business? Or is it more like some kind of tracker that just moves in realation to the market prices but you don't actually participate in the companies?