Wiring up the servo and trimpot is easy. You can use EITHER a 5V or 3V Trinket (or Gemma!)
The fastest way to get started is to have the servo powered by USB+ which is the 5V line from the USB port. This lets you get up to 500mA without going through the onboard voltage regulator. Then ground to GND. The control line of the servo goes to #0.
The outer edges of the trimpot go to GND and 5V or 3V (whichever is available on the Trinket) and the middle pin goes to #2
Connect the Trinket to the computer USB for power and programming!
You may solder the included header pins onto the Trinket to aid in attaching the board to a breadboard. The Trinket connects to power and ground (via the BAT pin) as well as the red and black (or red and brown) on the servo. The outer legs of the potentiometer also connect to power and ground (one to each, it is not polarity sensitive). The center leg of the potentiometer is connected to Trinket GPIO #2. The signal wire (yellow or orange) on the servo connects to Trinket Pin #0.
Normal or extra-long header pins can be placed on the breadboard to help you connect the servo to the board.
It is suggested you use an external wall or battery supply and not power the servo via the regulator. Servos can draw up to 500mA and the Trinket regulator can only source 150 milliamps (USB power generally 500 milliamps). The female DC adapter is helpful in connecting power supplies with barrel connectors to breadboards.