You can only use the CBX bridge if you:
- Are legally able to enter Mexico or the United States, depending on your direction of travel, and
- Have a boarding pass for a flight which:
- Departs from TIJ within the next 24 hours, or
- Arrived at TIJ within the last 2 hours
- Purchase a CBX ticket
Except for the requirement to buy a ticket for the CBX, and the boarding pass requirement, it works much the same way as any other airport border crossing.
In particular, unlike at land border crossings, on entering Mexico you will speak to Mexican immigration officers and be required to have a visa if nationals of your country require a visa to visit parts of Mexico other than the US border area. Because CBX is intended to serve people flying in and out of TIJ, either to points further in Mexico or to international destnations, it's not considered part of the US border adjacent area where many people would be visa-exempt.
If you need a tourist card, you should pick it up from Mexican immigration at CBX. Flights out of TIJ to elsewhere in Mexico are domestic, and you won't be able to obtain one afterward (which can cause you a lot of headache later!).
Because of this, CBX is not a good crossing point for people who are merely visiting Tijuana.