Do I just spray and wait or is it not that simple

 

Yes spray and watch it dissolve tar. I assume that's what you are using it for.

 

It's best to use when the car is wet I have found. A good tip I was told if there is lots is to spray it on then use paper towel to let it soak for longer and then wipe of after and make sure you rinse really well after use. It will also strip any protection on your paint.

 

Spray it on, let it do its thing for about 3 minutes or so, then wipe off with a MF towel. If you have some larger/persistent spots, spray some Tardis onto your MF and work it gently and it should lift. For larger chunks repeat the process.

Don't let it dry and don't use it on hot panels or direct sunlight where possible.