*Here there be spoilers, but only little ones*
It's been a while since the confirmation that Tom Holland's Spider-Man would be making his debut in [Captain America: Civil War](tag:994409), but people are still debating the extent of his involvement, and which side he's going to be on in the ensuing battle as the heroes are split over the proposed registration act resulting from the Avengers' actions in Nigeria.
This will be the first official appearance of Spider-Man as part of the Marvel Cinematic Universe. Given that until recently Sony held the rights to the character, both the Tobey Maguire and Andrew Garfield iterations of our friendly neighbourhood Spider-Man did not appear as part of the MCU but existed as part of a separate narrative universe (which is a very 'comic book' way of going about it, so funnily enough the different versions kinda work).
The current popular rumour is that Spidey is going to be going up against the titular Captain America in Civil War, which makes perfect sense given the source material.
As the [Marvel: Civil War](tag:2346746) begins Spider-Man supports Tony Stark, he even publicly unmasks himself in what is one of the most important scenes of the comic. Given that at this stage Spidey's Peter Parker identity was still one of the best kept secrets of the Marvel universe, this was a huge deal; a significant moment for the character and a meaningful move in the propaganda of the war.
But though he's initially on the pro-registration and Iron Man's side, Spider-Man becomes increasingly disillusioned with the war as it progresses, particularly following the death of Goliath (Bill Foster) during a clash of the two factions. When he learns that Stark and Richards (Mr Fantastic - who won't be appearing in the movie) are locking up the anti-registration heroes in the Negative Zone prison he fights with Iron Man before quitting to join Captain America's anti-registration movement (though not before getting the crap kicked out of him).
So on the flip side, it would also make perfect sense if he was to be fighting Tony Stark/Iron Man instead, as he appears on both sides of the battle and fights with both characters in separate scenes.
Just because we've seen him fighting Cap doesn't necessarily mean that he's going to be on Stark's side for the duration of the film, though sadly I doubt that there will be adequate time to explore this plot point fully, which is a real shame.
Spider-Man is, in my opinion, one of the most important characters in Civil War (aside from the two heads of our warring factions of course) because he functions as an ideological figurehead and eventual victim of the battle. He represents all the other heroes caught in the battle, torn between their beliefs, their freedom and their friends.
Unfortunately, given that Holland's Spider-Man has only just been announced as an official MCU character, we're currently lacking the background necessary for including him in a significant manner. But Civil War could be the thing that sets up Spider-Man's next film, as even after everything is done and dusted the war has violent repercussion for Peter Parker. Whilst he is left regretting his decision to reveal his identity, the Kingpin has his Aunt May shot and she ends up in a coma, prompting Spidey to react in an uncharacteristically violent manner.
Anyway, at the moment, what will happen in Civil War is really all just educated guessing as Marvel are keeping a pretty tight lid on details which, for a movie of this nature, is certainly a good idea.