You want to watch all Spider-Man movies, but you are not sure about the order or if they are connected? Here is a quick explanation.
There are Eight Spider-Man movies in total and they are divided into three groups. The first one is the Sam Raimi Spider-Man trilogy (2002-2007) starring Tobey Maguire. In the second group are two Marc Webb Amazing Spider-Man films (2012-2014) starring Andrew Garfield. This is the reboot of the Spider-Man series and it is completely independent from the previous movies.
Finally, the last two are Jon Watts films Spider-Man: Homecoming and Spider-Man: Far from Home starring Tom Holland, and these two are parts of the Marvel Cinematic Universe. This was a second reboot in the Spider-Man movie series and again, it is completely independent from the others.