This is the final boss fight of the game: the Venom-Spider-Man showdown on the top of Trask Tower. Venom will be attacking Trask in the helicopter on the right side of the rooftop. Go after him, but use your dodge to miss his tentacle grabs. Venom will try and slam you to the ground any chance he gets, so get used to dodging. All you really have to do is run at him dodge when indicated and hit him with a nice 4 hit combo ending in a launcher to set up some distance. Then repeat this and also hit him with the adrenaline rush when you get the chance (Nintendo DS version).
When he gets low on health, he'll start trying to eat you to regain his health and drain yours. When this starts, just try and keep more distance between you and Venom and continue the run, dodge, then attack strategy.