Here are some examples of diffusion.
Two simple examples:
just put some cloth dipped in perfume in a room and wait for a while you will be able to smell the perfume in other corner. it is similar to when someone wearing perfume passes you by.
this is a little gross example, but if you wear shoes and your feet sweat a lot, then at the end of the day, as you remove the socks, you are able to smell the odor.
Both of these situations are examples of diffusion where the gaseous molecules have diffused from higher concentration to a lower one.
You can find more examples on diffusion here: