We are installing a shower, sink and toilet in the basement. Do these need to be vented?
How do you vent them?

Yes, they all need venting. Before I give you more advice than you want try looking for an existing vent pipe. Do you have a slop sink or washer drain in the basement? You can T into their vent.

We are installing a shower, sink and toilet in the basement. Do these need to be vented?
How do you vent them?

Let me show you a typical bathroom drainage and vent layout. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book.
More questions? I'm as close as a click. Good luck, Tom