Se is enjoying the present moment and fully living in it. Not thinking about future consequences but experiencing action in the immediate. For instance you're at a club and there's a person that's eyeing you and such. You get fully raptured in the moment and do what you feel or think is right in the present. Flirting, saying hi, hitting the dance floor. On the other end of the spectrum Ni would think, "what can I achieve in the future? What should be my next step? Will we go back to the apartment for an ONS? Exchange phone numbers and have a relationship?" Se doesn't think about these things. It just does and is aware of everything happening in the here and now and soaking in ALL the details.
Si compares past experiences and senses to present circumstances. For instance my granddad drives me to church every week. There are certain places he's aware of and compares to past experiences. We pass a diner and he says, "Look at that! The parking lots packed! They're always packed there at this time." Or we pass a field where there's been geese in the past and he being it up and says, "I wonder if there will be geese this time," and looks for them. Like he does this every time. lol He remembers everything that's happened in past drives and checks to see how this new drive relates to those past experiences. Like exactly what changes or stays the same.
Completely different functions.
