Achieving spectacular combos in Tony Hawk's Pro Skater 1 + 2 is what makes the game so fun to play. Linking up long grinds and performing spinning aerial walks through dangerous obstacles is where you'll find the thrill of skateboarding.
Almost everything you can do is customizable, from the types of holds and grinds you can do to special tricks you can perform. Having said that, it's not obvious how the Special Counter works in the game, especially if you're unfamiliar with the original games.
First, to build the special counter, you just need to successfully perform standard tricks. It doesn't take long to fill up the Special Meter, and once it's there you can try out a bunch of special tricks that can rack up huge combos. They will require more button presses and time to land successfully, but will also offer a higher reward for your effort.
To see what special moves you can perform, head to the pause or main menu, then go to the skater tab. Here there will be a cheats option, with five places to start that include two-way links that you need to use to start the cheat. For example, if you bind the 360 Varial McTwist to Down, Left, and the flip button, using this combination while your special meter is full will perform the trick for you.
These can be tied to any button combination you want, with a huge selection of special tricks that can then be attempted on any level.
When you remove them, you will hear a beep which will indicate that you are using a special move, and display the name of the turn in yellow at the bottom. Match them together in more towers for huge points.