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I'm very new to both circuits and CircuitLab. It's pretty fun to do this, especially the simulator feature so I can make changes and see what they really do. I did get my first circuit working:

It's a simple circuit to control an LED from a Jetson TX1 GPIO pin. It was exciting to get the right values in the resistors and transistor and wire it all up and then see it working correctly.

Here's my question: I'm trying to design a version of this circuit that powers not a simple LED, but rather, a relay. This relay's coil needs 24V, and my Jetson has a power output of 5V, so I'm using a DC to DC step up to boost the voltage. The unit I'm using is a THM 10-0515WI.

How do I put this into my Circuitlab circuit? I would love to simulate it somehow.

Take a look at: https://www.circuitlab.com/circuit/qpj32v9dkp5w/temp/
which shows your design somewhat modified to drive a relay. For the simulation you could simply change "PWR" to 24 volts but since you may be wedded to the DC to DC step up converter I've shown a possible simulation for it which would work for circuit lab. The diode across the relay coil is very necessary as without it the coil inductance of the relay would generate a high voltage transient on turn-off which would almost certainly damage the transistor. The THM 10-0515WI which you are using is a design with high isolation between input and output which was intended for medical work where such isolation may be very necessary. If you are designing something for a medical application be very very careful as you could be open to substantial liability. Otherwise you may be paying for something you don't need.