I'd like to build a robotic arm...

Looks like you are heading in the right direction. A few small points that you may already be aware of:

The diagram doesn't show it but the ground side of the +6v power supply must be connected to the Arduino and servo grounds.

The diagrams shows numbers on the servos with the +6v line marked as 1, note that servo power is usually be the middle wire.

The Arduino pin are marked PWM – the arduino PWM output, analogWrite, should not be used to drive the servos. Any digital pin can be used.