This article or plot contains spoilers from the actual game. If you do not wish to be spoiled, do not read it.
Gotta Go Fast (Travel) is a mission in South Park: The Fractured But Whole.
After you discover the first Fast Travel Flag located outside of Cartman's House, Fastpass will send you an alert message, telling you to discover the Fast Travel Flag on South Park Main Street. Once you do so, the Fast Travel system will be fully functional, and Fastpass will become available as an ally in battle.
Head up to Main Street and activate the Fast Travel Flag located next to Tom's Rhinoplasty. Fastpass will arrive and explain the Fast Travel system; activating an active Fast Travel Flag will summon him to carry you to any other active Fast Travel Flag in South Park. He'll also join you as a Combat Buddy, so be sure to try him out the next time you get in a fight.
For now, you can only Fast Travel between Cartman's House and Main Street, but you will find more Fast Travel Flags later on. Note that some will only appear after certain story events, too (such as the one outside Token's mansion).
Note: Alternatively, you can unlock other Fast Travel Flags, but the Main Street one is the nearest, if Flags are unlocked in other places, cut scenes above will still ensue, with different backgrounds.
Be aware of the Chaos Minion at the right of Tom's Rhinoplasty; he will initiate a fight if you get closer to him. If you do end up fighting him, be careful around the Chaos Exploder (wearing full masks of tinfoil that cover everything but their eyes); when beaten, they will detonate themselves, affecting an area all-around them (8-tile area).